[ ]Amy was cleaning her room ,her friends came in.Awhen Bas

A 或 C 都可以吧
cleaning 为延续性动词.
从句动作和主句动作同时发生,且从句动作为延续性动词时,when,while,as都可使用.
①When ／While ／As we were dancing,a stranger came in．（dance为延续性动词）当我们跳舞时,一位陌生人走了进来.