Sometimes I doubt whether it is worthso.A. to work;hardB. to work;hardlyC. working;hardD.

问题补充：

Sometimes I doubt whether it is worthso.

A. to work;hard

B. to work;hardly

C. working;hard

Dworking;hardly

答案：

A. to work;hard

B. to work;hardly

(答案→)C. working;hard

D. working;hardly

解析：句意：有时我怀疑是否值得这么努力地工作。Be worth doing意为“值得做某事”；hard为副词修饰动词work；故选C。