题干
Faced with financial uncertainty, the family decided to____ their trip to Europe to save money.
A：call off
B：call for
C：call i
D：call o
答案(点此获取答案解析）
A
A：call off
B：call for
C：call i
D：call o
满足
，且
的导函数
，则
的解集为（ ）
