A:Fe+O2 点燃__ FeO2
B:NaOH+CuSO4=Cu(OH)2↓+Na2SO4
C:2CO+O2 点燃__ 2CO2↑
D:2Mg+CO2 点燃__ 2MgO+C
____ is not good to play computer games so much. (That/It)
设an=1nsinnπ25,Sn=a1+a2+⋯+an,在S1,S2,⋯,S100中,正数的个数是( )