A:when did he go abroad
B:why he is going abroad
C:how soon will he be back
D:how long he will stay abroad
关于声音,下列说法正确的是( )
①升高温度 ②加入正催化剂 ③增大反应物浓度 ④将块状固体反应物磨成粉末 ⑤增大压强.