Just like children, baby animals spend countless hours at play. After studying animal play for many years, scientists recognize that young animal play is practice for adult behavior. Today this play is roughly divided into the following groups.
Locomotor play refers to the movements animals carry out in their play.  Running, leaping, turning, and kicking are some of the most common examples of locomotor play.  An adult deer may  run, leap, and twist(曲折前进) to escape its attackers.  Play movements like these surely make  young animals nimble. Someday these skills might help save their lives.
Moving forward slowly, attacking suddenly .and biting are examples of predatory play that help  young predators(食肉动物) prepare for a life of running after and taking hold of other animals.  Wild cats, wolves, and bears are predators. It is very common to see these young animals play this  kind of games which sharpen their skills and teach them about their strengths and limitations.
For children, playing with toys is both fun and educational. It helps improve their hand and  eye movements as well as develop hand skills to accomplish tasks. It is the same with animals.  Young chimpanzees improve their hand skills while playing with sticks. Birds also play with things  in ways that teach. Swallows drop and recover feathers in mid air. Diving suddenly to catch the  feathers is good practice for catching flying insects.
Social play helps animals learn how to behave when they run into other animals. And it teaches  animals about communication. An animal gives signals to let another animal know it wants to play.  Many animals give signals by showing a " play face" .  In some ways this face is like a human smile; the animal holds its mouth in a relaxed and open manner.  During play-fights, some animals may step backwards to signal that they are playing and not acting seriously.
Until now, scientists have understood playful acts help prepare animals for their serious adult situations.  But the numbers of playful species and examples of animal play are vast.  The purpose of animal play may have meanings scientists have not discovered yet.
The main purpose of the text is to ______.

A．ask us to take good care of wild animals

B．encourage us to learn more about animals

C．entertain us with interesting animal stories

D．show us something about animal behavior

The underlined word "nimble" in Paragraph 2 can best be replaced by______.

A．cruel	B．swift
C．curious	D．strong

Which of the following belongs to predatory play?

A．A deer runs, leaps, and turns.

B．A chimpanzee plays' with a stick.

C．A lion moves slowly and makes an attack suddenly.

D．A dog holds its mouth in a relaxed and open manner.

Based on Paragraph 5, a " play face " is______.
A. a type of signal between animals
B. a name for a kind of animal play
C.  an activity that involves adult animals
D  an action that is taught to another animal
Which of the following shows the structure of the text?