普通砂岩普氏硬度系数一般为（）。
A.f=1～2
B.f=2～3
C.f=4～6
D.f=7～9
参考答案：C
He was told that it would be at least three more months _____ he could recover and return to work.
A．when
B．since
C．before
D．that
— When will you come home for dinner? I'll prepare it for you.
一 Don't _____ it. I'll eat out with my friends.[ ]
A. care about
B. worry about
C. bother about
D. talk about
