Living in the wild can be hard. Finding food and staying safe aren't easy. Each day, animals struggle to survive in their habitats. Not all animals get by on their own. Some animals form a close partnership with other kinds of animals. These pairings are called symbiotic (共生的) relationships.

    In a symbiotic relationship, the animals depend on each other. One animal helps the other meet its needs. Sounds good, right? Not always. Some animals are not very kind to their partners. In some cases, one animal meets its needs but hurts its partner. Take ticks, for example. These insects suck blood to live. To get blood, they attach themselves to other kinds of animals. Ticks can pass germs that cause disease instead of helping their hosts.

    In other relationships, animals don't treat their partners so poorly Both animals benefit from living with the other animal.

    Small animals called cleaner shrimps have found a way of helping fish at coral reefs. As their name suggests, the shrimps clean the fish. They hang out at what scientists call a cleaning station. A fish stops by. Then a shrimp climbs onto the fish and even steps into the fish's mouth. The shrimp uses its tiny claws to pick stuff off the fish's body. That can include dead skin, tiny pieces of food, and wee creatures that can hurt the fish. The fish gets a nice cleaning. The shrimp enjoys a tasty meal offish trash.

    Small birds called plovers are also in the cleaning business. They have big customers—crocodiles. Crocs have long snouts（鼻子）filled with sharp teeth, Cleaning them is tricky. When a croc opens its mouth, the plover hops right in. The croc does not snap its snout shut. Instead, it lets the plover eat small, harmful animals attached to its teeth. The plover gets an easy meal while the croc gets clean teeth.

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    There's no doubt that water is vital to any life. About 60 percent of the average adult human body is made of water. This includes most of your brain, heart, lungs, muscles and skin, and even about 30 percent of your bones. Yet there's little scientific agreement about the exact amount of the stuff an individual should consume each day. So how much water do you actually need to drink to be healthy?

    You may have heard that you should drink eight 8-ounce glasses of water a day. Yet, the downside of this rule, researchers say, is that drinking water by the glass is not the only way that humans take in it. The “8 X 8” rule essentially overlooks two big sources of daily water consumption. One such source is food. Everything you eat contains some water. Watermelons, for example, are more than 90 percent water by weight. Different diets naturally contain different amounts of waters, and the counts. The other key water sources are other beverages. Non-alcoholic drinks such as coffee, and tea, contain mostly water and all contribute to your hydration（水量）.

    So, between all the food, water and other fluids you consume in a day, how much water should you aim to take in?

    The National Academics of Sciences suggests that woman consume a total of approximately 2.7 liters (91 ounces) of warm from all beverages and foods each day and men 3.7 liters (125 ounces). But these are just general guidelines.

    The truth is, there is no magic standard for hydration—everyone's need vary depending on their age, weight, level of physical activity, general health and even the climate they live in. The more water you lose, the more water you'll need to replace with food and drink. If you are looking for concrete advice, though, the best place to look is within. Drink up when you're thirsty.

    Feet help us walk, run, dance, and jump. The words feet and foot are also used in everyday speech.

    To be under someone's feet means to be troublesome. In other words, you are standing too close to someone and are getting in their way. Some adults criticize (批评) children for being under foot.

    Speaking of children, if someone says their home will soon have the pitter-patter of tiny feet, it means the family is expecting a baby!

    Now, people who are active do not let grass grow under their feet. They are never in one place for very long. People who can think and take action at the same time are said to be able to think on their feet.

    Some people appear to have it all. They have money, a good education, good looks, a great family and a large circle of friends. You could say they have the world at their feet. This means whatever they want seems to be there for them.

    People who have both feet firmly on the ground are realistic and practical. They are not dreamy. You might say such a person is well grounded. If you are a bad dancer, you might be described as having two left feet. To dance well, it is better to have a right foot and a left foot.

    Sam loves skiing. He thinks that it would be fun to own a ski resort (滑雪场) high in the mountains. But he knows nothing about running a business. So, he decides to get his feet wet. In other words, he wants to get used to a new situation.

    He joins an organization for resort owners and attends their meetings. He travels to ski areas all over the United States. This helps Sam get his foot in the door. Having a foot in the door is a starting point. This expression comes from people selling things door-to-door. They would block the door with their foot so people couldn't close the door on them.

    The easy way out isn't always easiest. I learned that lesson when I decided to treat Doug, my husband of one month, to a special meal. I glanced through my cook book and chose a menu which included homemade bread. Knowing the bread would take time. I started on it as soon as Doug left for work. As I was not experienced in cooking, I thought if a dozen was good, two dozen would be better, so I doubled everything. As Doug loved oranges, I also opened a can of orange and poured it all into the bowl. Soon there was a sticky dough (生面团）covered with ugly yellowish marks. Realizing I had been defeated, I put the dough in the rubbish bin outside so I wouldn't have to face Doug laughing at my work. I went on preparing the rest of the meal, and, when Doug got home, we sat down to Cornish chicken with rice. He tried to enjoy the meal but seemed disturbed. Twice he got up and went outside, saying he thought he heard a noise. The third time he left, I went to the windows to see what he was doing. Looking out, I saw Doug standing about three feet from the rubbish bin, holding the lid up with a stick and looking into the container. When I came out of the house, he dropped the stick and explained that there was something alive in out rubbish bin. Picking up the stick again, he held the lid up enough for me to see. I felt cold. But I stepped closer and looked harder. Without doubt it was my work. The hot sun had caused the dough to double in size and the fermenting yeast(酵母) made the surface shake and sigh as though it were breathing. I had to admit what the living thing was and why it was there. I don't know who was more embarrassed(尴尬) by the whole thing—Doug or me.

    As Artificial Intelligence(AI) becomes increasingly sophisticated(复杂的), there are growing concerns that robots could become a threat. This danger can be avoided, according to computer science Professor Stuart Russell, if we figure out how to turn human values into a programmable code.

    Russell argues that as robots take on more complicated tasks, it's necessary to translate our morals into AI language.

    For example, if a robot does chores around the house, you wouldn't want it to put the pet cat in the oven to make dinner for the hungry children. "You would want that robot preloaded with a good set of values," said Russell.

    Some robots are already programmed with basic human values. For example, mobile robots have been programmed to keep a comfortable distance from humans. Obviously there are cultural differences, but if you were talking to another person and they came up close in your personal space, you wouldn't think that's the kind of thing a properly brought-up person would do.

    It will be possible to create more sophisticated moral machines, if only we can find a way to set out human values as clear rules.

    Robots could also learn values from drawing patterns from large sets of data on human behaviour. They are dangerous only if programmers are careless.

    The biggest concern with robots going against human values is that human beings fail to so sufficient testing and they've produced a system that will break some kind of taboos(禁忌).

    One simple check would be to program a robot to check the correct course of action with a human when presented with an unusual situation.

    If the robot is unsure whether an animal is suitable for the microwave, it has the opportunity to stop, send out beeps(嘟嘟声), and ask for directions from a human. If we humans aren't quite sure about a decision, we go and ask somebody else.

    The most difficult step in programming values will be deciding exactly what we believe in moral, and how to create a set of ethical rules. But if we come up with an answer, robots could be good for humanity.

In the movie, The Day After Tomorrow, many climate changes including an ice age are caused by global warming. Much of the science in the movie has been questioned by people. However, there may be some truth to the idea in the movie that global warming could cause an ice age.

The theory starts with an understanding of why Europe and Scandinavia are not colder already. After all, other places at the same latitude(纬度) are covered with ice. The ocean current called the Gulf Stream brings warm waters from the Caribbean to the UK and Europe. These waters warm the countries around their path. This is why the UK, Europe and Scandinavia have a warmer climate than Alaska. Global warming has nothing to do with this. Global warming is significant. It could slow the Gulf Stream, or even stop it. If this were to happen, the cold waters would stay in the area of Europe, the UK, Scandinavia and the Northeastern US. It could mean an ice age for those regions.

Some weaknesses in the Gulf Stream could happen for different reasons. These days, it could happen due to global warming, caused by human activities, such as the burning of fossil fuels.

If a new ice age happened, it would probably be caused by the melting of the polar ice. This will lead large quantities of cold and fresh water to come into the ocean, which would disrupt the Gulf Stream and cause the cooling of many areas that now have a mild climate.

Scientists have gathered a lot of data from the oceans and the land to try to determine whether an ice age could be caused by global warming. With all this information at hand, it appears that it is indeed possible that global warming could lead to an ice age.