how many teeth?

Newborn babies do not usually have any teeth．Their front teeth begin to grow when they are about six months old．Most children have all their“milk”teeth by the time they are two years old．There are 20 teeth altogether． 新生婴儿一般没有牙齿。当6个月时他们的前牙开始生长。大部份小孩到了2岁就会长出所有的乳牙。一共有20只牙齿The front teeth are used to cut food by biting．The back“double”teeth are used to grind up the food．This makes the food easier to swallow． 前牙用来在咀嚼时咬断食物。后面的两只牙用来磨碎食物。这样使得食物更容易被吞下。Foods that are sticky and have a lot of sugar in them will make holes in the teeth if the teeth are not cleaned with a brush． 如果饭后不用牙刷刷牙,很粘的和很甜的食物会使得牙齿长洞The“milk”teeth start to fall out when children are six or seven years old．The new teeth that grow in their place have to last for ever!当小孩6到7岁时乳牙开始脱落。然后新的牙齿就会长出来,而且永久保持著