选出与其他三项不是同一类的单词。(6分)
( )(1) A. boy B. student C. girl
( )(2) A. big B. teacher C. small
( )(3) A. tree B. nurse C. doctor
( )(4) A. zebra B. zoo C. panda
( )(5) A. Ben B. boy C. Helen
( )(6) A. mother B. brother C. school