They knew nothing about ______ he was a thief.
The number of air crashes that _______ in developing countries _________ increasing.
Bill suggested ________ a meeting on what to do for the Shanghai Expo during the vacation.
_________many times, he finally understood it.
This morning, I rushed to the library, only ________ that its door was still locked.
_______ with so much trouble, we failed to complete task on time.