题干
------I don’t know why he has made such a silly mistake in the exam.
------ He ____________ it before he handed in the paper.
------ He ____________ it before he handed in the paper.
A：may have checked
B：might check
C：must have checked
D：should have checked
答案(点此获取答案解析）
D
的图象为C，
关于直线
对称;②函数
在区间
内是增函数;
的图象向右平移
个单位长度可以得到图象