根据短文选择正确答案

    Today is a holiday. Sam is playing football in the park. Amy is playing the guitar（吉他）under the tree. Daming is flying a kite. Lingling isn't here. She visits her grandma today. The children are playing merrily. They think life is like a dream.

A：How many horses do you have?

B：Four．

下列有关对人体消化系统的描述中，不正确的是（　　）