| 阅读理解。 |
| At night, bats fly through the air, catching hundreds of insects and other small animals. But during the day, they hardly move at all. Instead, bats pass the time hanging upside down from a secret spot. There are a couple of reasons why bats rest this way. First of all, it puts them in a position for takeoff. Unlike birds, bats can't fly into the air from the ground. Their wings don't produce enough lift to take off from a dead stop, and their hind legs are so small and underdeveloped that they can't run to build up the necessary takeoff speed. Instead, they use their front claws to climb to a high spot, and then fall into flight. During the hours when most enemies are active, bats gather where few animals would think to look and most can't reach. This allows them to disappear from the world until night comes again. There's also little competition for these resting spots, as other flying animals don't have the ability to hang upside down. Bats have a unique physiological adaptation that lets them hang around this way without using any energy. For you to hold your fist around an object tight, you contract (紧缩) several muscles in your arm, which are connected to your fingers by tendons (腱); as one muscle contracts, it pulls a tendon, which pulls one of your fingers closed. A bat's talons (爪) close in the same way, except that their tendons are connected only to the upper body, not to a muscle. To hang upside down, a bat pulls its claws open with other muscles. To get the talons to take hold of the surface, the bat simply lets its body relax. The weight of the upper body pulls down on the tendons connected to the talons, causing them to hold tight. Therefore, the bat doesn't have to do anything to hang upside down. |
| 1. Bats hang upside down because ______. |
| A. they haven't developed a pair of strong claws B. they can't start to fly from the ground directly C. they have no hind legs to support their body D. they can't find quiet places to stay during the day |
| 2. The third paragraph tells us that bats' hanging upside down _______. |
| A. is to save their energy for night movement B. is a way to fight against flying animals C. is a great way to hide from danger D. is a skill to compete for the flying places |
| 3. Why can bats hang upside down easily? |
| A. Because their upper body is light. B. Because they have strong muscles. C. Because their talons are linked to muscles tightly. D. Because their tendons are linked to their upper body. |
| 4. What is the passage mainly about? |
| A. The living habits of bats. B. How and why bats hang upside down. C. The importance of bats' hanging upside down. D. How bats use their energy at night. |