The man stopped from time to time_______whether he was being followed.
There is only one of the oldest customs that ________ in this district up to now.
Modern teaching equipment as well as tens of computers _______ to the village school last week.
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.