We should read more good books because they can ______our eyes．

Scientists say it may be five or six years ______ it is possible to test this medicine on human patients.

“______ the friendship between our two people last forever!”, and with this sincere hope, the president concluded his speech.

I don’t know when my son back, but when he back, I’ll call you.

The boy has poor eyesight because of _______ computer games.