In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

[Q]: Article: 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 several muscles in your arm, which are connected to your fingers by tendons ;as one muscle contracts, it pulls a tendon, which pulls one of your fingers closed. A bat's talons 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.
Answer: they can't start to fly from the ground directly
[A]: Bats hang upside down because _ .

[Q]: Article: At first, the earth's surface layer was made up of huge blocks of hard, solid rocks. Then slowly, the rocks broke up into smaller and smaller pieces. Finally stones, pebbles and grains of sand were formed. Many sorts of plants and animals lived and died on the surface of the earth. Their remains mixed up with the stones, pebbles and formed soil. The outmost layer of the earth is soil. There are many ways in which large pieces of rock break into smaller ones. Wind, water, heat and cold help to break up rocks. When winds blow grains of sand against a large rock for a long time, the softer layers of the rock are slowly worn away. These leave holes and cracks in the rock, which become bigger and finally the rock breaks up into smaller pieces. The moving water of streams and rivers also helps to break up rocks. As the water moves along, it carries with it small pieces of rock. These rub the larger ones. Thus, the larger rocks are worn down to smaller pieces. The heat of the sun is also helpful to breaking up rocks. When the sun shines, the rocks become very hot. If these rocks are suddenly cooled, they may crack. Ice also plays a part in making soil. Water in the cracks can turn into ice in cold weather. As this happens, it becomes bigger and the cracks become wider, and finally break into smaller pieces.
Answer: forms very slowly
[A]: According to the passage, soil _ .

[Q]: Article: Birds in cities are damaging their health by trying to sing above the noise of urban life. New research shows that male birds are trying to compete against traffic and city sounds.They are now singing louder and at higher frequencies,which could harm their vocal cords .Some birds are choosing to sing at night instead of during the day.This makes them more open to attack and also creates stress and exhaustion. "The difference between urban and rural birdsong is becoming so big that the two groups could now be unable to communicate.This could lead to inbreeding and a weak gene poo1."said Dr Sue Anne Zollinger of the.University of St Andrews. According to Zollingar,a bird group with a small gene pool might adapt less quickly to new diseases and could be wiped out. A study of the dawn chorus found that birds in Berlin sang up to 14 decibels louder than those in the forest.The birds sang loudest on weekday mornings. "By trying to sing over the sound of the city,birds ale rising vocal injury,"said Zollinger."All this puts the same strain on a bird's vocal cords as when a human need to shout to be heard--except that the birds are doing it all day,every day,"she said. "Singing under such pressure means birds have less control over the sound they produce.Their songs may lose quality and become more rough--sounding."said Zollinger.This could make them appear less attractive to female birds. Mark Constantine,author of The Sound Approach to Birding,said:"Birdsong is important for our quality of life and has been proved to reduce our blood pressure.When we live in the centre of large,urban areas,we get stressed and it's extremely good to have birdsong around us.The impact on humans of birdsong is massive.It harms us,as well as the birds,if their songs become louder and simpler.
Answer: they have to frighten their enemy away
[A]:
Some birds in cities now choose to sing at night time because _ .