—I it right here a moment ago. But it's gone.
A:did you put; have put
B:had you put; have put
C:have you put; put
D:were you putting; had put
美国独立战争的转折点是( )
已知数列an为等比数列,且a4·a6=2a5,设等差数列bn的前n项和为Sn,若b5=2a5,则S9=( )