题干
．— Shall we attend the concert this evening?
— Great idea, _____ we can do some shopping first．
A：if
B：before
C：since
D：whe
答案(点此获取答案解析）
A
A：if
B：before
C：since
D：whe
的公比为正数，且
·
=2
，
=1，则
=（ ）
