Carol said the work would be done by October personally I doubt very much.A. itB. thatC.

问题补充：

Carol said the work would be done by October, personally I doubt very much.

A. it

B. that

C. which

D. when

答案：

A. it

B. that

(答案→)C. which

D. when

解析：考察定语从句。Which指代上文的the work would be done by October这件事情，在句中作doubt的宾语。