鲨鱼的尾属于()。
A.正尾
B.圆尾
C.歪尾
D.以上都不是
参考答案:C
_____ some mammals came to live in the sea is not known. [ ]
A. Which
B. Since
C. Although
D. How
我国发现最后一例脊髓灰质炎野病毒病例是在哪()年
A.1994
B.1998
C.2000
D.1995