Hi there, when I was in elementary school long ago, I was taught that the main idea is usually in the first or last sentence of a passage, so I'd go with letter a. because b. it is stated in the first paragraph isn't specific on what setence it's in. c. it can be in the last paragraph but this isn't specific if its on the last sentence. And d. main idea is never found in the bodynof the text, as I was taught in elementary school. A. is the answer because main idea isn't always directly stated in a passage.
Hope this helps,
-Wolfs :)
