脑疝形成的基础是下列哪项
A．颅内压增高
B．脑水肿
C．颅内占位性病变
D．颅腔各部分之间存在着压力差
E．脑外伤
参考答案：D
一个精原细胞经过减数分裂产生的精细胞数目是 [ ]
A．1个
B．2个
C．4个
D．8个
English is popular around the world and most people speak it _____ a second language. [ ]
A. as
B. like
C. for
D. by
