我国使用“长征3号甲”运载火箭的动力是由高氯酸铵(NH4ClO4)分解所提供的,反应方程式为2 NH4ClO4N2↑+Cl2↑+4X↑+2O2↑,则X的化学式为( )
A:NH3
B:H2
C:H2O
D:HCl
— Children today find it hard to focus on study.
— Exactly, as they ________ so many fun things to do.
在武则天和唐玄宗时都担任重要职务的是( )