问题
选择题
It's the first overseas trip that President Hu Jingtao has made this year,_______?[ ]
A. is it
B. isn't it
C. has he
D. hasn't he
答案
答案：B
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It's the first overseas trip that President Hu Jingtao has made this year,_______?[ ]
A. is it
B. isn't it
C. has he
D. hasn't he
答案：B
2NH3(g)，在637 K、30 MPa下n(NH3)和n(H2)随时间变化的关系如图所示．下列叙述正确的是