D

Unlike your heart and brain, your teeth weren’t there ready to work from the day you were born.

Although babies begin to grow their first tooth even before they are born, you can’t see babies’ teeth until they are about 6 or 7 months old.

After that first tooth comes out, more and more teeth begin to appear. Most kids have their first set of teeth when they are 3 years old. These are called baby teeth, and there are 20 in all. When a child grows to 5 or 6, these teeth start falling out, one by one.

The baby teeth fall out because the permanent teeth (恒牙) grow and take the place of the baby teeth. By the age of 14, most kids have lost all of their baby teeth and have a full set of permanent teeth.

There are 28 permanent teeth in all — eight more than the original set of baby teeth. At about the age of 20, four more teeth call ed wisdom teeth usually grow at the back of the mouth. And you have all your 32 teeth.

根据短文内容，选择最佳答案，并在答题卡上按要求作答。

(   )66. When a baby is born, ________________________.

A. he has 20 teeth to work for him

B. his teeth haven’t begun to grow yet

C. one can’t see his teeth

D. he has only a few teeth

(   )67. A baby has his first set of teeth when he is about _____________.

A. 3 years old    B. 4 years old      C. 5 years old    D. 6 years old

(   )68. From the passage we can know that permanent teeth _____________.

A. are a s many as baby teeth      B. are 8 more than baby teeth

C. begin to grow at the age of 14     D. will be replaced by wisdom teeth

(   )69. One will have _________ teeth in all when he is about 20.

A. 20     B. 24     C. 28       D. 32

(   )70. Which of the following is TR UE?

A. At the age of 14, one has two sets of teeth—baby teeth and permanent teeth.

B. If you have a good habit, you won’t lose your baby teeth.

C. Wisdom teeth usually grow in the front of the mouth.

D. Your head and brain are ready to work for you when you are born.