In general, multiplying a function by some constant k will stretch its graph vertically by a factor of k if k>1, or shrink its graph vertically by a factor of k if k<1. In this case, k=2>1, so statement A is true.
The function [tex]f(x)=2\sqrt{x}[/tex] only accepts nonnegative inputs (so its domain is x>=0), and its outputs span all the nonnegative real numbers (range y>=0). This is also true of [tex]f(x)=\sqrt{x},[/tex] so statement C is also true.
