题干
He didn't go to school yesterday __________ he was ill.
A：because
B：because of
C：if
D：when
答案(点此获取答案解析）
A
He didn't go to school yesterday __________ he was ill.
A：because
B：because of
C：if
D：when
是定义在区间
上的函数，且
，则方程
在区间