According to _____ survey conducted last month,_____ fourth

According to _____ survey conducted last month,_____ fourth of the post.90’ s college graduates
According to _____ survey conducted last month,_____ fourth of the post.90’ s college graduates prefer online job-hunting.
A.a; a B.a； the C.the； a D.the； the
正确答案是A.为什么不是C呢?survey 后有给出特定的时间,那么survey应该是特指,那就应该用the啊为什么会用a呢?