I haven’t learned to ride a bike yet. I _______ twenty minutes ago.

My friend Bob just bought an apartment in a suburb of Beijing last week, which is much smaller than oursbut is three times _____ expensive [ ]

We were required not toanyimportant details before it was made public.

Now lots of teenagers spend a lot of timeplaying computer games.——Yes. Teachers and their parents shouldprevent them ______________ too much.

Only by increasing the number of doctors by 50 percent ________ properly in this hospital. (2013·大纲全国，32)