①Swifts live mostly in the air. These small birds are among the fastest animals on Earth. In fact, swifts can go two or three days without touching the ground! To get used to life in the sky, swifts use their speed and the saliva in their mouths.
②Swifts can fly faster than 100 miles per hour. That's because their wings are like boomerangs. This shape of the wings helps them to fly much faster. They can also move one wing faster than the other, which allows them to make sharp turns without slowing down. Making fast, sharp turns helps swifts catching flying bugs to eat.
③The saliva helps swifts catch bugs to feed their young. It is sticky, like glue. Swifts often fly into clouds of bugs such as mosquitoes and open their wide mouths to catch as many insects as they can. The bird collects insects in its mouth graduallyand holds the insects in a sticky ball of saliva. One food ball can contain nearly 1,000 bugs.
④Swifts also use their saliva as glue to build their nests. The birds catch feathers in the air and stick the feathers together to build a strong nest on the side of a cliffor building. Swifts' short feet are not good for walking or standing on land for long. But their sharp claws allow them to stick to rocks and walls so they can take a brief rest before returning their lives in the sky.
B . 
C . 
D . 
