题型:阅读选择 题类:模拟题 难易度:容易
广东省汕头市潮南区2018年初中毕业生学业考试模拟英语试题
Animals can move from place to place, but plants cannot. When an animal is under attack, it can run away or fight back. Plants certainly cannot run away, and they have no teeth or claws. But plants can protect themselves in both physical and chemical ways.
Some plants have their own ways to keep animals away. For example, the leaves of the holly(冬青) have sharp prickles(刺) that discourage grass-eating animals. Holly leaves on lower places have more prickles than leaves on upper places. This is because the lower leaves are easier for most animals to reach. Some plants, such as the oak trees(橡树), have thick and hard leaves that are difficult for animals to eat. Some grasses may contain a sandy material, and eating such grasses wears down the animals' teeth. Many plants also have chemical defenses. Some plants produce chemicals that taste bitter(苦) or cause an unpleasant reaction. Some plants may fight against an attack by increasing the production of these chemicals. When a worm bites a tobacco leaf (烟叶), the leaf produces a chemical smell. Many plants depend on both physical and chemical defenses. A certain plant in China, for instance, has prickly leaves, and each prickle has poisonous water(毒液). Only one experience with this kind of plant will teach an animal to stay away from it in the future.
Have you ever rubbed your hands together when they get cold? Why do we do that? We do that for friction. Friction happens when two things that aren't very smooth rub together to make heat energy. The faster you rub two things together, the more friction (and heat) you can make. Let's discover friction!
WHAT YOU'LL NEED: ● Soap ● Water ● Your hands! WHAT TO DO: 1. Make sure your hands are dry. 2. Rub your hands together until you feel the heat of your hands. 3. Now, use soap and water to get your hands very slippery (滑的). 4. Try to make friction happen while your hands are slippery. 5. Please write down what has happened. LET'S TALK! Friction is an energy that happens when two things rub together. When friction happens, it makes heat! When your hands are slippery, they won't make very much friction and your hands won't get so hot. DID YOU KNOW? 1. Friction happens when you stop your fast running bike. 2. Ancient people made fires by rubbing two pieces of wood together. Friction happened though they didn't know it. ? Friction is everywhere. Have you ever noticed situations where friction is happening? If not, ask your parents to take you out in a car. If it is not too hot, touch the tires (轮胎) of the car before and after a short drive to see how much warmer they get from friction. |
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