According to_______ World Health Organization,health care plans are needed in all big cities to prevent _____spread of AIDS.
All the students in this school are required to ________ at least two lectures on how to study every month.
Your desk is covered with too many unnecessary things, including used papers and books. You’d better ________ some of them.
On arrival at the flood-stricken village, the PLA soldiers set ______ rescuing the villagers.
He gave us another piece of advice, ________ of great help to the research work.
Only when _____ in the afternoon _____ able to leave.