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