____直到……时候
指从过去某一点到从句所示的时间为止的一段时间。如:
By the time we got to his house, he had finished supper.
在我们到达他就已经吃完了晚饭。
读图,回答下列问题
① Look at the pigs. ____ A. Baa…baa…!
② It’s a white sheep. ____ B. Moo…moo…!
③ I can hear a horse. ____ C. Oink…oink…!
④ I have a duck. ____ D. Neigh…neigh…!
⑤ I can see a cow. ____ E. Ouack…quack…!
选择恰当的应答语( )
已知数列{an}的通项公式为an=log2n+1n+2n∈N*,设其前n项和为Sn,则使Sn<-5成立的自然数n有( )