问题
选择题
Tom _____ the USA. He _____ back in two months. [ ]
A. has gone to; comes
B. has gone to; will be
C. has been to; comes
D. has been to; will be
答案
答案：B
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Tom _____ the USA. He _____ back in two months. [ ]
A. has gone to; comes
B. has gone to; will be
C. has been to; comes
D. has been to; will be
答案：B
2PbSO4+2H2O回答下列 问题。（不考虑氢、氧的氧化还原）