Which is a clue to the main idea of a text

It is easy to identify a main idea that is directly expressed in the text. Main ideas are often found at the beginning of paragraphs. The first sentence often explains the subject being discussed in the passage. Main ideas are also found in the concluding sentences of a paragraph.

absolutism the political belief that one ruler should hold all of the power within the boundaries of a country.

i also think it is d (sorry if it's not)