Usually, when people write, they tend to get confused about the correct use of commas in a sentence or a text. This is because people tend to believe that commas are used for pause, much like a period. But the reality is that this is not so. Use it before a linking word like but, of, etc, to connect two independent sentences or clauses. The second case is much like in this example; commas are used to divide dependent clauses. Also, and most importantly for this case, commas are used to divide items that make part of a series. So, the correct answer is C: The former astronaut gave an inspiring, opening address to the crowd of excited, fascinated, students, because words like inspiring, and fascinated are words of a series used to describe and amplify the information regarding a main issue. So, for example, inspiring describes the opening address and then the second clause, which talks about the group of students, both excited and fascinated are working as descriptors of the students. This is why you use commas in these places.