if i pass my driving test,I---a car

if i pass my driving test,I___a car
A.would buy
B.were to buy
C.shall buy
D.shll have bought
C )
我判断这个是对将来的虚拟
但是根据虚拟条件句用谓语:should/were to+动词原形
主句用谓语:would/should/could/might +动词原形
老说 也应该是选择 ( A
为什么选择C