Which sentence tells the main idea of paragraph 2 "In a CME, billions of tons of the sun's

corona, or outer layer, blast out into the

solar system all at once."

"Solar flares are brief but powerful bursts

that send great amounts of radiation into

space."

"The sun also produces more violent

types of space weather."

"Coronal mass ejections, or CMEs, are

even more spectacular events."

C. "The sun also produces more violent

types of space weather."

Explanation:

It's good to know that the main idea of the paragraph is usually its first sentence, while the rest of the paragraph only provides more details. However, since this isn't necessarily always the case, let's analize this paragraph.

Two types of space weather are mentioned, solar flares and coronal mass ejections and their brief definitions are given. This shows that these two solar events are only further explanation of the types of the space weather and they serve as the evidence for the argument that space weather can be very violent.

Since the rest of the passage serves as an elaboration of the first sentence, that makes it the main idea of the passage.