Many people who saw the film were afraid to swim in the sea when they remembered the scenes

     people were eaten by the shark.

A. when    

B. on which    

C. at which

D. where

下列各组物质中

 ③CH₃CH₃和CH₃CH₂CH₂CH₃ ④ H₂和T₂

⑤ 与 ⑥CH₃－CH₂－OH和CH₃－O－CH₃

互为同位素的是；____________； 互为同素异形体是：____________；

互为同分异构体是：____________；互为同系物的是：____________。