the answer is options C and D
When you are checking over your work and solution, you C) want to make sure you include the correct units so that the answer makes sense in the context of the question and D) see if the answer is reasonable. For example, if I say 2(3)+1=6839, does this make sense? No, especially because the numbers in the question are small integers and could not result in such a large value.
-E :)