Which best identifies an element of an effective summary?

a. it includes a direct quote

b. it includes your opinion

c. it includes the main ideas of the source article

d. its is written in first-person point of view

C, because a summary is a makeup of the main ideas of an article or piece of work.

I think your answer is gonna be C, because a summary is; a brief statement or account of the main points of something.

Just think about when you read the back of a book before you check it out

798 calories are in 6 10-ounce bottles of Apple juice. We have to calculate how many calories are in one 10-ounce bottle of Apple juice. We have just to divide 798 calories by 6: 798 : 6 = 133. There are 133 calories in one 10-ounce bottle of Apple juice.
Hope this helps. Let me know if you need additional help!