儿童长期吮拇指可造成（）
A.前牙开
B.牙弓狭窄
C.腭盖宽大
D.前牙深覆盖
E.上牙前突拥挤
参考答案：A, B, D, E
There are 450 birds at a small zoo. The number of birds is 5 times the number of all the other animals combined. How many more birds are there than non-bird animals at the zoo ？（）
A. 400
B. 360
C. 270
D. 180
E. 90
对外汉语教学的基本形式（）。
