Only when your identity has been checked__________.

Only in recent years ______ begun to realize that wild dogs, kept within bounds, often do more good than harm.

So difficult______ it to acquire a large vocabulary without the help of a teacher that he was close to giving up .

I was surfing the Internet _____of successful rendezvous and docking of Shenzhou-VIII   and Tiangong-I.

Rarely         so much media attention, for the performance has left the audience breathless with excitement.