How can we keep our teeth (21) ______? Firstly, we ought to visit our (22) ____ twice a year. Secondly, we should brush our teeth (23) ____ a toothbrush and fluoride toothpaste at least twice a day, once after breakfast and once before we go to bed. We can also use toothpicks (24) _____between our teeth after a meal. Thirdly, we (25) ______ eat food that is good (26) ______ our teeth and our body: milk, fish, brown bread, raw vegetables, fresh fruit, etc. 21. a. health b. healthy c. healthily d. unhealthy 22. a. dentist b. doctor c. teacher d. engineer 23. a. on b. of c. by d. with 24. a. clean b. to clean c. cleaning d. to cleaning 25. a. should b. ought to c. need d. a & b 26. a. for b. at c. on d. to