I counted the people          the activity, and there were 286 of them.

A．were taking part in

B．taking part in

C．taken part in

D．took part in

（1）现有五种物质：

①O₂和O₃

②CH₃CH₂CH₂CH（C₂H₅）₂和CH₃CH₂CH₂CH（CH₃）C₂H₅

③¹²C 和¹⁴C

④CH₃CH₂CH₂CH₃和（CH₃）₂CHCH₃ 

⑤乙烷和丁烷．     

互为同系物的是______，互为同分异构体的是______互为同位素的是______互为同素异形体的是______

（2）请根据官能团的不同对下列有机物进行分类，并把正确答案序号填写在相应横线上      

  ①芳香烃______②卤代烃______③醇______④酚______ ⑤醛______    ⑥酮______  ⑦羧酸______   ⑧酯______．