绿色食品指的是（　　）

     My friend Tony is an American1 . He is ten years old. He lives 2  his family in China now. There are 3  people in his family; his mother Mrs Green, his father Mr. Green and his little sister Amy. He has a white cat. 4  name is Betty. Look ! Amy is playing 5  Betty. His father, Mr. Green,is watc­hing TV. His mother is doing housework. What about Tony? He is doing6 Chinese homework. He can't 7   Chinese well, but he likes Chinese very much.
    Tony's 8 works in a TV station. His father works in a school as an9 teacher. Tony and his sister10 to the same school.

一个有理数与它的相反数的积（    ）