求教补充题54

54.   Tenor George Shirley sang more than 20 leading roles at the Metropolitan Opera since having his debut there as Fernando in Cosifan tulle on October 24, 1961.

(A) sang more than 20 leading roles at the Metropolitan Opera since having

(B) sang more than 20 leading roles at the Metropolitan Opera since having had

(C) has sung more than 20 leading roles at the Metropolitan Opera since

(D) has sung more than 20 leading roles at the Metropolitan Opera after（C）

(E) has sung more than 20 leading roles at the Metropolitan Opera subsequently to

为什么用since而不能用after引导呢？

since用完成时 after用一般过去时呀