Which one of the following statements about a topic sentence and main idea is accurate

a. a topic sentence is the central idea of a paragraph, while a main idea is the central idea of an entire text.

b. a topic sentence and a main idea are always the same thing.

c. a topic sentence is found in the introduction, while a main idea is found in the conclusion.

d. a topic sentence does not change a position, but the main idea can be found in multiple places.