Which sentence correctly uses commas to separate phrases? the cooking class will teach us how to, grill fish, bake a pie, and make cream. the math test will include one word problem, one graph and ten equations. i spend my free time reading books, watching tv, and playing video games. staying fit involves eating healthy foods, staying active and, sleeping well.

The correct answer is C, "I spend my free time reading books, watching TV, and playing video games."  

A comma is needed to separate items in a list. It does not need to go before the list, but should be included before and (although there are people who believe this comma is not necessary). Also remember that all of items in your list must be in the same tense (present, past, or present progressive).