下列均为筋瘤的发病原因，除了：（）
A.筋脉薄弱
B.久立
C.经常负重
D.久坐
E.妊娠
参考答案：D
— Dad, can you tell me why so many students choose to study abroad at a very young age?
— _ ___,darling. I have never thought about it. [ ]
A. Take your time.
B. You've got me there.
C. Don't be silly.
D. Bad luck.
关于Ca2+通过细胞膜转运的方式，下列哪项描述正确
A．以单纯扩散为主要方式
B．以易化扩散为次要方式
C．有单纯扩散和主动转运两种方式
D．有易化扩散和主动转运两种方式
