you have worked out the first problem you may go on to work on the second. A. Even if B.

问题补充：

you have worked out the first problem, you may go on to work on the second.

A. Even if

B. Unless

C. Now that

D. Though

答案：

A. Even if

B. Unless

(答案→)C. Now that

D. Though

解析：考查连词：A. Even if即使B. Unless除非C. Now that既然D. Though虽然，句意：既然你已经算出了第一个问题，你可以继续算第二个问题。选C。