**Explanation**

The correct answer to the question "Is he going to sell tickets?" is option **b) yes, he is**. This choice indicates that the person in question will indeed sell tickets.

There are a few reasons why option B is the correct answer:

**Subject Pronoun Agreement**
- The pronoun "he" is used in the question, indicating that the question is asking about the actions or intentions of a male individual. Therefore, the response should also include the pronoun "he" to maintain subject-verb agreement.

**Understanding the Question**
- The question is asking about the future actions of a specific individual, i.e., "he." It is important to pay attention to the specific wording of the question and choose the response accordingly.

**Elimination of Other Options**
- Option A states "yes, she is." However, the question is specifically asking about a male individual, so this option can be eliminated.
- Option C states "yes, he isn't." This response is contradictory and does not make sense in the context of the question. It implies that the person is both going to sell tickets and not going to sell tickets, which is illogical.
- Option D states "None of these." While it is important to consider all options before choosing an answer, in this case, option B, "yes, he is," is the only response that aligns with the question and makes logical sense. Therefore, option D can be eliminated.

In conclusion, the correct answer to the question "Is he going to sell tickets?" is option B, "yes, he is." This response maintains subject-verb agreement, aligns with the question, and eliminates other illogical options.