Answer: C)
Explanation:
If the person is discussing about morally right for keeping animals in zoo on the internet that would be quite formal way because it is an online discussion and the person is talking about their own opinions on something.
It is not informal or very informal because the topic is referring to formal discussion and ideas because it is considering importance of animals and moral rights.
Since it is online, it can't be taken so seriously as it can be when you are talking eye to eye with someone. When you are talking or discussing with someone online, you don't have to follow some rules that you need to follow when you are discussing in person.
