30. Even if you are an experienced teacher, you sometimes ____ make some mistakes.
__________ he took part in the competition, he won a second prize.
I still remember __________ chess in class by my teacher about twenty years ago.
As is known, mobile phones make it possible for people to __________ each other conveniently.
A large amount of money __________ robbed in the bank and it shocked the government greatly.
The manager says he needs an assistant that he can __________ to deal with the problems that may occur in his absence.