Rik-rrork. That's the sound made by frogs singing at night. You might have thought the noises were just the musical sounds of ure. You probably didn't realize that you were listening to frogs' communicating with one another. These familiar sounds are not random(随意的) but are actually meaningful to frogs.

Being Heard but Not Seen

    Frogs are good at being heard but not seen. These animals have several characters that protect them n predators (捕食者 ). One is their size. Most frogs are small, which helps them hide easily. Many frogs have coloring that allows them to hide in their environment, making it difficult for predators to find them. In addition, most frogs are active at night. So it is difficult for most animals to see them in the dark.

Small but Loud

    Frogs call to tell other frogs where they are. Their voices can be very loud. But when frogs feel the footsteps of a larger animal, they become silent.

    Many of the world's frogs live in rain forests, where there are many different animals calling to their own species (物种 ) in their own ways. Frogs need to call loudly enough to be heard through the noise in order to find other frogs.

Singing with Purpose

      Peter Narins is a scientist who studies how frogs call to one another. He has learned that frogs use their calls to help them tell friend from enemy. They sing the same notes at the same volume (音量 ) each time they call. In addition, Narins has found that frogs of the same species always sing the same patterns (模式 ). These patterns are like a code that is different from other animals' calls and difficult for others to copy. Narins also observed that timing plays a role in frog calls. Many frogs call only at a certain time of night.

More Work to Do

    Scientists want to better understand the purpose of frog calls. Studies continue to explore the details of frogs' unique communication. Being heard but not seen is one way frogs stay safe. The idea that they have found a way to survive in a dangerous world is simply amazing.

    Bananas are the perfect snack. Not only are they sweet and delicious, but they are easy to carry around, so you can take them anywhere. Best of all, bananas provide different things that the human body needs!

    Bananas grow best in warm places that get lots of rain. They grow on plants that look like trees.

    The banana plant, however, is considered a herb rather than a tree because it doesn't have a strong, woody stem(茎，干). The plants can grow as high as 30 feet. When they reach their full height, flowers grow out from the stem. These flowers produce bananas.

    Two or three times each year, the plants produce fruit. The bananas grow together, which seem like "hands". A hand is made up of 10 to 20 bananas. Growers sometimes call bananas "fingers".

    Each bunch(丛) of bananas has about 15 hands, and so a whole bunch may have as many as 200 bananas and can weigh more than 100 pounds.

    After about three months, the bananas are ready to be picked. At this point, they still aren't the sunny yellow color of bananas. Farmers pick them when they're green. That's how they're shipped to stores. They turn yellow along the way and are ready to be sold.

    If you love bananas, you've got a lot of company. Americans have been enjoying bananas since the first shipment arrived in the United States in 1876. Today, American eat more bananas than any other fruit. More bananas are sold than apples and grapes together. Every American eats over 26 pounds of bananas each year!

    Americans were shocked to discover that the national bird was in danger of disappearing from the skies forever. Studies in 1970 showed only about 1,000, or fewer, bald eagles(秃鹰) in the country.

    The major cause of the problem was people. The spread of civilization(文明) destroyed many of the eagles' feeding and nesting areas. And the eagles were being affected by D-D-T and other insect poisons. The poisons were in the animals the eagles ate. They reduced the eagles' ability(能力) to use calcium(钙). This made the outside of the eagles' eggs very thin. Often, the eggs broke before baby birds were developed.

    In 1972, the U. S. government banned(禁止) D-D-T. People also became interested in protecting places where eagles live. And stronger efforts were made to carry out laws protecting the birds. Scientists began a program that placed baby bald eagles which were born under human care, into nests of wild bald eagles. Often, the wild birds accepted the babies.

    These efforts appear to have been successful in saving the American bald eagles. Today the number of the bald eagles has increased to more than 11, 000.

House fires cause many deaths each year and a large number of these fires are unfortunately set by children.{#blank#}1{#/blank#}Kids must understand that they'd better not play with fire. You should keep matches and lighters out of their reach.

{#blank#}2{#/blank#} The main job of such an alarm is to protect you while you're asleep. You should have a smoke alarm outside each bedroom and on each floor of your home. You ought to have two plans for getting out of your house if there is a fire and practise these plans in the dark with your family.

A smoke alarm warns you of the danger. {#blank#}3{#/blank#}Take action immediately. When you come to a closed door, check it with the back of your hand. If it feels hot, there may be smoke or fire behind the door, so take care. Once you are out of your house, call the fire department from a neighbor's house. If a family member or a pet is caught inside, you shouldn't go back in. Firemen know how to perform rescues safely.

{#blank#}4{#/blank#} Change the batteries at least once a year. You should use the test button each month to see if the alarm and batteries are still working. A smoke alarm lasts about ten years. You ought to change it even if it seems to be working.