Đáp án:

Giải thích các bước giải:

21. Read these sentences about ___ your teeth healthy.

A. keep B. you keep C. to keep D. keeping

22. Do the following things ___ healthy teeth.

A. to have B. having C. for havingD. have

23. Avoid ___ a lot of sweet.

A. eating B. to eat C. eat D. for eating

24. It's important ___ tooth decay.

A. avoid B. avoiding C. to avoid D. avoided

25. You can also improve your teeth if ___ healthy food.

A. to have B. having C. you have D. have

26. Unfortunately, you cannot stop tooth decay simply by ___ your teeth.

A. you brush B. brushing C. to brush D. brushed

27. One way to stop tooth decay is ___ less sugar.

A. to eat B. for eating C. you eat D. you are eating

28. Fluoride toothpaste helps ___ tooth decay.

A. preventing B. prevented C. to prevent D. for preventing

29. Many coutries have also started ___ fluoride to drinking water.

A. add B. with adding C. they add D. to add

30. They have proved that fresh fruit ___ teeth healthy.

A. to keep B. keep C. keeps D. keeping

21D

22A

23A

24C

25C

26B

27A

28A

29D

30C