A(n)
clause should always be separated from the rest of the sentence by commas.

did , cooked , was reading , will do , will prepare , will read

explanation:

but it is sometime nessary to hit key points or subjects   but is sometimes to much reveiw if there was a way to slim down the redone work it would improve for every body.

there are many stores that have sales right before christmas

i think it is c. good luck!