曲面x^2+4y^2+z^2=4与平面x+z=a的交线在yOz平面上的投影方程是( )。{
A A.<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23817744_0.png"> B
B.<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23817744_0_1.png"> C
C.<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23817744_0_2.png"> D
D.(a-z)^2+4y^2+z^2=4