The answer to that question is them. The class is a collective noun for a bunch of students that are learning from a teacher. Since we are referring to people, then we cannot use it because the noun it is used for inanimate objects. Pronouns like them are used to refer to people
The answer is c, the wax was melted by the sun.
Definitely not B or D. A is out of the question too, so I think it's C
