Hello!
First of all, I totally understand why this one is confusing! Many people use these terms interchangeably, and they really shouldn't! Here is a breakdown of why each answer is right or wrong:
a) The majority of the talk was
This one is incorrect because it misuses the word "majority." In English, we should use the word majority when talking about more than half of a group of people/animals. Majority shouldn't be used to talk about the amount or volume of something. We can say that a majority of college students worry about exams, but we can't say the majority of the exam was difficult.
b) The greater part of the talk was
This one is correct. It uses the right terms to describe how much of the talk itself is devoted to that particular topic. Since "part" is often used to break down inanimate objects or concepts, this one is right!
c) The bulk of the talk has been
Again, this is a common word that's misused in English. "Bulk" should only refer to the size/volume/weight of an object - not to a percentage of something. Since the subject (the talk) isn't something with a set size/weight, we can't use bulk here.
d) A large amount of the talk has been
Much like C, using the word "amount" is wrong. It suggests that giving a talk has some kind of volume or weight you can measure, which doesn't really make sense. Only use "amount" for discussing the volume, weight, or size of something.
e) A predominance of the talk was
The word "predominance" means that there is more of something in the world than others, and should only be used to refer to a plural subject. You can't say that only one thing (the talk) is a predominance of something - there's only one. You could say, "There was a predominance of talks at the convention about the scientific method," which means most of the talks (plural) at the convention were about one topic.
I hope this helps! I'm available if you'd like any follow up.
