1. "This is the chicken's comb." is correct. It is not incorrect to say "This is the comb of the chicken.", but it is the way a teacher might speak, and is more formal and academic. 2. "These are a bird's feathers." is correct. Again, it is not incorrect to say "These are the feathers of a bird", it is just more formal. 3. "These are buffalo horns." is correct. Again, "These are the horns of buffalo." is not incorrect, it is just more formal. By the way, the plural of buffalo is usually buffalo. Also, your question was not grammatically correct. it should have been : "If I point at a chicken, should I say, "This is the chicken's comb.", or "This is the comb of the chicken."? Or can I say both? The same mistakes in 2 and 3.

Yes you can. Although to make the sentence more economical, I would write : "Unfortunately, the disadvantages cancel out all the advantages listed above."

"one" refers to the writer. The sentence means that if the writer is careful to respect his/her audience, then he/she can write what he/she wants - in this case, presumably, by portraying "people as a sort of freak show".

Your example is correct. Here are some more examples. I told him off for leaving the house in a mess. The teacher told the children off for not listening to her. We were told off by the life guard for diving into the swimming pool. "You should tell Dave off for being such a nuisance." "If you don't tell them off, they'll just keep on doing it!"

They are both correct. The first sounds awkward, while the second flows well. Personally, I would always use the second.

A student deferment means that as long as a student maintains his status as a student his obligation to do military service will be postponed. In this case, presumably, it was necessary to get A's to to maintain the right to deferment.

"it's not about me." means that the speaker is not the centre of interest. In the first example the speaker is saying that the "great work" was great because of the work itself, or because of others who also worked. The key point being that it was not what he/she did that was of importance. In the second example, the speaker is saying that whether or not he/she can do "another three months" is not related to his/her ability or availability, but is related to other factors (which we don't know). In the third example, the speaker is saying that it is Adrian, not him/her that is the cheater.