Swifts （雨燕） 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 （唾液） in their mouths.
Swifts can fly faster than 100 miles per hour.That\’s because their wings are like boomerangs （回力镖）.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 catch flying bugs to eat.
The 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 as many insects as they can.The bird collects insects in its mouth gradually （逐渐地） and holds the insects in a sticky ball of saliva.One food ball can contain nearly 1,000 bugs.
Swifts 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.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 short rest before returning to their lives in the sky.
（1）The second paragraph mainly talks about ______.
A．how fast swifts can fly
B．how swifts turn around in the sky
C．why swifts make sharp turns
D．why swifts can fly and turn so fast
（2）What does the underlined word "It" refer to in Paragraph 3? ______
A．The saliva.
B．The air.
C．The shape.
D．The speed.
（3）Which of the following is True about swifts? ______
A．They don\’t usually live on land because of wings.
B．They can fly for a long time because of their small bodies.
C．They can\’t walk for a long time because of their short feet.
D．They can catch nearly 1,000 bugs in one go with the saliva.
（4）Which of the following best shows the structure of the passage? ______
A．
B．
C．
D．