When you have the same subject that initiates two actions, you CANNOT separate the subject and the verbs with a comma.
For instance, "Sally likes apples and hates oranges" [Correct]
"Sally likes apples, and hates oranges" [Incorrect]
Let's first ignore other mistakes that choice C) has. In the example we have above, C) says "supplicants who (subject) were (verb1) either asking the goddess Bona Dea’s aid in healing physical and mental ills, and thanking (verb2) her for helping." Clearly the usage of comma here is incorrect because it separates the same subject and verbs.
-- by 会员 silent7706 (2010/5/21 23:03:07)