题目

关于力的作用，下列说法中正确的是                                                              （    ）       A．用拳头击打墙壁，拳头感到疼痛，说明墙壁对拳头有作用力       B．用拳头击打棉花包，拳头不感到疼痛，说明棉花包对拳头没有作用力       C．打篮球时，接球时对手有作用力，手对球没有作用力       D．打篮球时，接球时球对手有作用力，手对球也有作用力The local government announced that only when the fire was under control ________ to return to their homes. A．the residents would be allowedB．had the residents been allowedC．would the residents be allowedD．the residents had been allowed