During the 1990s, American country music has become more and more popular.
We often speak English in class.
One-third of the students in this class are girls.
To swim in the river is a great pleasure.
It is necessary to master a foreign language.（it作形式主语，真正的主语为后面的不定式）
Smoking does harm to the health.
The rich should help the poor.
How to do well is an important question.
Early to bed and early to rise makes a man healthy.
When we are going to have an English test has not been decided.
That he isn’t at home is not true. (that不能省略)