已知线段a,求作等边三角形ABC,使AB=a,作法如下:①作射线AM;②连结AC、BC;③分别以点A和点B为圆心,以a的长为半径作圆弧,两弧交于点C;④在射线AM上截取AB,使AB=a.其合理顺序为( )
A:①②③④
B:①④②③
C:①④③②
D:②①④③
Our teacher says reading in the sun isn’t good _______ our eyes.