某不纯的硝酸铵中氮的质量分数为36%,则此硝酸铵中混入杂质可能是[ ]
A.NH4HCO3
B.(NH4)2SO4
C.CO(NH2)2
D.NH4Cl
答案:C
No one makes Mr. Green _____ so much work. But you can always find him _____ very late. [ ]
A. to do; working
B. do; to work
C. to do; to work
D. do; working
由于变频器具有电子热保护功能,一般情况下可不接______。