$\text{31. D }$

$\rightarrow$ First, we ought to visit our dentist twice a year ( 2 lần một năm -> 6 tháng/ lần ) 

$\text{32.D }$

$\rightarrow$ we should brush our teeth with a toothbrush and fluoride toothpaste at least twice a day once after breakfast and once before we go to bed

$\text{33. A }$

$\rightarrow$ We can also use wooden toothpicks to clean between our teeth after a meal.

$\text{34. B }$

$\rightarrow$ we should eat food that is good for our teeth and our body: milk, cheese, fish, brown bread, potatoes, red rice, raw vegetables and fresh fruit

$\rightarrow$ A : loại cakes, chocolate 

$\rightarrow$ C : loại cakes 

$\rightarrow$ D : loại cakes 

$\text{15. B }$

$\rightarrow$ Chocolate, sweets, biscuits and cakes are bad, especially when we eat them between meals.

$\rightarrow$ A : loại fish 

$\rightarrow$ C : loại fish , potatoes

$\rightarrow$ D : brown bread

31. How often should we visit the dentist?

A. Every 3 months

B. Every year

C. Every 4 months

D. Every 6 months (First, we ought to visit our dentist twice a year)

32. How often should we clean our teeth?

A. At least once a day

B. At least 3 times a day

C. At least four times a day

D. At least twice a day (Secondly, we should brush our teeth with a toothbrush and fluoride toothpaste at least twice a day once after breakfast and once before we go to bed)

33. Why do we use toothpicks?

A. To clean our teeth after a meal (We can also use wooden toothpicks to clean between our teeth after a meal.)

B. To make our teeth more beautiful

C. To protect our teeth after a meal

D. To hide the food between two teeth

34. Three kinds of food that is good for your teeth

A. Fish , cakes , chocolate

B. red rice, fresh fruit, brown bread (Thirdly, we should eat food that is good for our teeth and our body: milk, cheese, fish, brown bread, potatoes, red rice, raw vegetables and fresh fruit.)

C. milk , cakes , potatoes

D. red rice, cakes, brown bread

35. Three kinds of food that is bad for your teeth

A. Fish , cakes , chocolate

B. biscuits , cakes , chocolate (Chocolate, sweets, biscuits and cakes are bad, especially when we eat them between meals.)

C. Fish , cakes , potatoes

D. sweets, cakes, brown bread

Mong đc 5 sao+ctlhn+cảm ơn