I

1, The more he works, the more tired he feels.

2, I spent half an hour walking to school yesterday.

3, We have learned English since we were in grade 3.

4, Do you ever meet a more difficult test than this?

5, How high is your brother?

II

1, My mother often goes walking with friends in the park.

2, Nam and I have studied hard since last weekend.

3, Many rare plants and animals are in danger because we are destroying the environment.

4, If we use recycled paper, we will save a lot of trees.

5, Air in the city is more polluted than the air in the country.