①同时闭合声控开关和光控开关电灯才能亮;
②三孔插座单独接入。
—Look! All students in the classroom are preparing for the coming exams_____.
—Yes, the exams are very important to them.
238-32÷4×5=( )
天花病毒对人体来说( )
①抗原
②抗体
③传染源
④病原体