OG11 Verbal 86

90. Since 1986, when the Department of Labor began to allow investment officers’ fees to be based on how the funds they manage perform, several corporations began paying their investment advisers a small basic fee, with a contract promising higher fees if the managers perform well.

(A) investment officers’ fees to be based on how the funds they manage perform, several corporations began

(B) investment officers’ fees to be based on the performance of the funds they manage, several corporations began

(C) that fees of investment officers be based on how the funds they manage perform, several corporations have begun

(D) fees of investment officers to be based on the performance of the funds they manage, several corporations have begun

(E) that investment officers’ fees be based on the performance of the funds they manage, several corporations began

The clause beginning Since 1986... indicates that the practice described in the second clause continued for some period of time after it began. Choice D, the best answer, supplies the present perfect have begun, which conveys this continuity; D also uses a construction that is appropriate when “allow” means “permit”: allow... to be based on. Choices A, B, and E incorrectly use the past tense began rather than the present perfect; furthermore, in each of these options, they has no referent, since officers is a possessive modifier of fees.
                        Choices A and C include the awkward phrase based on how the funds they manage perform. Choices C and E incorrectly use allow that...fees be based.

正确答案D的指代为什么没有歧义？