顺序练习
话题练习
题型练习
口语评分
写作评分
单科机考
A.
It commonly occurs in play but not in other activities.
B.
It applies only to animal species that do not hunt for food.
C.
It has been observed only in laboratory settings.
D.
It contradicts the play-as-preparation hypothesis
正确答案:AD
译文