We must cooperate to solve this problem.

They (referring to women or girls) are my best friends.

I like watching children play in the park.

The children are playing in the park.

Please try reading these books.

We will do our best to solve this problem.

We will do our best to solve this problem.

We must cooperate to solve this problem.

His acting has gone up a stage and grade.

There are various classes in this school.