选出与其他两个单词不同类的一项。
( )（1）A. ruler B. fish C. hen
( )（2）A. this B. that C. is
( )（3）A. Yes B. No C. not
( )（4）A. activity book B. story book C. pen
( )（5）A. cow B. horse C. animal
( )（6）A. camera B. fan C. elephant
( )（7）A. boy B. girl C. fan
( )（8）A. it B. who C. he