请教一道语法

the civil war put a financial burden on new york bussinessman, -------- on southern trade.

a)relied formerly

b)formerly had relied

c)they former;y relied

d)who had formerly relied

答案选d 我觉得选a,我觉的有who 不可以,因为为前面有逗号..如果d对,请告诉我a那里错了

a, 因为不是被动关系，所以不能relied，如果是relying就正确了。