A remarkable variety of insects live in this planet. More species of insects exist than all other animal species together. Insects have survived on earth for more than 300 million years, and may possess the ability to survive for millions more.
Insects can be found almost everywhere—on the highest mountains and on the bottom of rushing streams, in the cold South Pole and in bubbling hot springs. They dig through the ground, jump and sing in the trees, and run and dance in the air. They come in many different colors and various shapes. Insects are extremely useful to humans, pollinating (授粉) our crops as well as flowers in meadows, forests, deserts and other areas. But ticks and some insects, such as mosquitoes and fleas, can transmit disease.
There are many reasons why insects are so successful at surviving. Their amazing ability to adapt permits them to live in extreme ranges of temperatures and environments. The one place they have not yet been found to any major extent is in the open oceans. Insects can survive on a wide range of natural and artificial foods—paint, pepper, glue, books, grain, cotton, other insects, plants and animals. Because they are small, they can hide in tiny spaces. Some insects disguise like natural objects so as to ______.
A. frighten away their enemies B. avoid being discovered
C. send warning signals D. look bitter-tasting