GRE数学官方指南第六章中第11题什么意思,

GRE数学官方指南第六章中第11题什么意思,
Each of the following linear eauqtions defines y as a function of x for allintegers xfrom 1 to100.For which of the following equations is the standard deviation of the y-values corresponding to all the x-values the freatest?
a.y=x/3 b.y=x/2+40 c.y=x d.y=2x+50 e.y=3x-20