Mark against the correct answer in each of the following:

Mark against the correct answer in each of the following:

If the plane $2 x-y+z=0$ is parallel to the line $\frac{2 x-1}{2}=\frac{2-y}{2}=\frac{z+1}{a}$, then the value of $a$ is

A. $-4$

B. $-2$

C. 4

D. 2