A:①→②→③→④
B:②→④→③→①
C:②→①→④→③
D:②→③→①→④
—I think students should have mobile phones to call their parents.
— . They often use them to play games instead.
若函数fx=x2+2a-1x+2在区间(-∞,4上是减函数,则实数a的取值范围是( )