脊椎动物颈椎和荐椎的首次分化发生在（）。
A.鱼类
B.两栖类
C.爬行类
D.鸟类
参考答案：B
Mr. Wu is a teacher with _______. He often tells us some of his unusual _______ in America.
A．a lot of experience, experiences
B．much experience, experience
C．many experiences, experience
D．many experience, experiences
Protel 99SE为PCB编辑器提供的设计规则共分为（）类。
A.8
B.10
C.12
D.6
