题干
They _________to see you off at the airport, but they got there too late.
A：have hoped
B：had hoped
C：would hope
D：hope
答案(点此获取答案解析）
B
A：have hoped
B：had hoped
C：would hope
D：hope
产物不稳定，受热即脱水而生成不饱和醛． 
