When he_____there.a.returned to b.retured back c.returned

C

C

A选项，there 前不能加介词
B选项，return 后不能加back ,,如果要加back 的话，要把return 改成went

go back=return

C
return是及物动词，后面不能加介词back,应直接用return sp,或者用go back sp.