阅读理解。 It takes many years for you to grow up. There are two periods in your life when you grow rapidly. The first period begins right after you are born and lasts until you are about six months old. The second period starts when you reach the age of 13. First, girls grow faster than boys, then boys catch up and grow faster and stronger. Your head stops growing earlier than the rest of you. By the time you are ten, your head is nearly full size. The bones of your arms and legs are short when you are a baby. When you reach the age of nine, your bones starts to grow rapidly, and will keep growing until you reach your full height (高度). Besides growing taller, your body changes in other ways. When a boy is about 13 years old, his voice begins to get deeper and he may begin to grow a beard (胡子). At about the age of 13, a girl's body begins to function (运行) like a woman's. Some important changes are taking place, changes that makes it possible for boys and girls, when they are older, to become fathers and mothers. 1. The first period in your life when you grow very rapidly ______. [     ] A. lasts about thirteen years B. lasts about six months C. doesn't begin until you are about six months old D. begins when you are six months old 2. Your head nearly stop growing ______. [     ] A. when you are born B. when you are ten years old C. when you are thirteen years old D. when you are six months old 3. About the age of 13, a child ______. [     ] A. stops growing B. reaching his full height C. begins to grow a beard D. begins to change in other ways 4. The meaning of the last sentence is that ______. [     ] A. boys and girls are not sure to become fathers and mothers when they are old B. it is necessary for boys and girls to become fathers and mothers when they grow up C. boys and girls must have some important changes before they grow up D. it is important that boys and girls should become fathers and mothers when they are older