My friend Tony is an American   1  . 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 doing   6 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 an   9  teacher. Tony and his sister 10  to the same school.

实验小组用如图所示装置进行实验．

实数﹣$\frac{1}{2}$的相反数是（　　）