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
