Answer: a. A comparison of wedding rituals.
This is likely to be done only by cultural anthropologist.
Though cultural anthropologist can also study all of the above.
Explanation:
Cultural anthropology is the study of human culture. Cultural anthropologist are those that lives with people of different culture, they learn all about that culture, then compares the differences and similarities between them.
Once it comes to comparison of cultural activities, it can only be done by cultural anthropologist.
The study of artifacts are also done by anthropologist, sociologist,ethnologist, but the ones that are specially dedicated to that are the archaeologist.
So are all of the above, cultural anthropologist can be involved in all of the above. But the one most likely to be done only by cultural anthropologist are the comparison of wedding rituals.