问题
选择题
Ladies and gentlemen, please fasten your seat belts. The plane ________.
A．takes off
B．is taking off
C．has taken off
D．took off
答案
答案：B
考查时态。用现在进行时表将来。
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Ladies and gentlemen, please fasten your seat belts. The plane ________.
A．takes off
B．is taking off
C．has taken off
D．took off
答案：B
考查时态。用现在进行时表将来。
2NH3(g) △H2=－92.4kJ/mol