Passage 1 Questions 1 to 5 are based on the following passage. Hummingbirds include the smallest birds in the world, but they belong to one of the latest group of birds, the Trochilidae family. These birds are found in deserts, mountains, and plains, but most live in tropical rain forests. Their name refers to the humming sound made by their tiny, beating wings; each species creates a different humming sounds depending on the speed of its wing beats. There are 328 hummingbird species. The smallest is the bee hummingbird from Cuba, and the largest is the giant hummingbird from South America. Hummingbird bills （喙）come in different sizes and shapes, too. The long bill is adapted to collect nectar（花蜜）from flowers. The bill protects the long,split tongue and allows each hummingbird species to feed from specific types of flowers. Hummingbirds arc called nectarivores （食密类）, because about 90 percent of their diet is the nectar from flowers. They also snack on insects. A hummingbird hunts insects by flying and diving to snap them up out of the air. If a hummingbird sees a bird that it doesn't want in its territory, it gives a high-pitched warning and starts doing dive attacks. Other hummers and even birds of different species often join in to dive-bomb the unwelcome bird until it leaves. The hummingbird is fearless, as it can overcome everything unless taken by surprise. When it comes to flying, nobody does it better. Like a helicopter, a hummingbird can go up, down, sideways, backward, and even upside down! Most of its wings are made of hand bones instead of arm bones like other birds* wings. When hovering, the wings turn in opposite directions and then reverse themselves in a figure-eight movement. Hummingbirds also have muscles that power both the up and down stroke instead of just the down stroke, as in other birds. They can beat their wings from 20 to 200 times per second. Hummingbirds are such good fliers that most of them never walk. As tough as they are, hummingbirds still face a few clever natural enemies. Hummers have been caught by dragonflies, trapped in spider webs, and snatched by frogs. Other birds occasionally eat hummingbirds.In what way are hummingbirds unique compared with other birds?
A、They often walk.
B、They can go up and down.
C、Their wings are made of hand bones.
D、Their muscles can power the up stroke.
【正确答案】：D
【题目解析】：题目问的是如果蜂鸟与其他鸟类的不同之处。根据第四段的第五句话Hummingbirds also have muscles that power both the up and down stroke instead of just the down stroke, as in other birds.可知，蜂鸟的肌肉可以使蜂鸟的翅膀向上挥动和向下挥动，而不像其他鸟类那样只能向下挥动。因此选择D. Their muscles can power the up stroke.
