Choose the correct answer from the given four options. The distance between the lines $y = mx + c_1$ and $y = mx + c_2$ is
$\begin {array} {1 1} (A)\;\large\frac{c_1-c_2}{\sqrt{m^2+1}} & \quad (B)\;\large\frac{|c_1-c_2|}{\sqrt{1+m^2}} \\ (C)\;\large\frac{c_2-c_1}{\sqrt {1+m^2}} & \quad (D)\;0 \end {array}$