In the interests of boosting attendance, the Boston Baseball Club has lowered admission prices; baseball tickets have been priced to sell and they are.
A. have been priced to sell and they are - present perfect tense is used to describe an action that started in the past and is continuing in the present or its effects are continuing in the present. So, the usage of this tense is correct. The problem is the usage of 'they are'. In such sentences, always try to place the verb at the end of they are. If it makes sense, then it's usage is correct. Consider this:
tickets have been prices to sell and they are sell. Is this correct? Of course not. This option is incorrect for this reason.
B. are priced to sell, and they have - The verb 'are' is correct here. Now, repeat the process mentioned in choice (A) to find out whether the sentence makes sense.
tickets are priced to sell and they have sell. This is also incorrect. Option (B) can be easily eliminated for these reasons.
C. are priced to sell, and they do - This is the correct choice. Consider this sentence: tickets are prices to sell and they do sell. This sentence makes perfect sense!
D. are being priced to sell, and have - are being priced is present continuous verb, i.e., the action is happeningright now. Well, maybe not! Also, you can apply the test explained in option (A) to determine whether the usage of 'and have' is correct. You will find out that it is not.
E. had been priced to sell, and they have - past perfect tense 'had been priced' is incorrect as there is no other action happening in the past. verb they have is also incorrect.