There are a lot of computers in the lab,and they need professional __________ to make sure they can be in a good state.

--What on earth are the police busy with? ---They have been looking into how the plane crash _______.

Lei Feng always _______ the interests of the people _______ everything else, which has been praised highly by people all over the country .

 A huge fire ______ last night and many houses were burnt down.

— What happened then? — The Red Army _____ the bridge after they crossed it.