China began to open to the outside world in the late 1970s._________, there have been great changes in the country.
I think _______ a foreign language is not easy. You should _______ it often.
It’s important us learn English well.
One of my teammates fell ill _______ he can’t practice with us now.
—I’m sorry I my exercise book at home. —Don’t forget it here tomorrow,please.
—What are you going to do tomorrow? —_______ I _______ go hiking.