Hello. Unfortunately you did not submit the text that this question refers to. Without the text it is impossible for me to show you which answer option is the correct answer. However, I will try to help you find that answer as best I can.
There is only one way to find the correct answer, and that is by reading the text, and that is what you should do. When reading the text, you will be able to find its central idea, which is nothing more than the subject that the text is presenting. In that case, you will be able to find that subject when you identify what the author of the text is talking about, what he is presenting to the reader.