表皮细胞的更替时间一般认为是:
A.20天
B.28天
C.14天
D.7天
E.19天
参考答案:B
Do you know where my address book is? — It________ be in the hall cupboard. I think I saw it this morning.
A.could
B.can
C.will
D.must
使用成形刀时,怎样减少和防止振动