Answer:
Choice B) {-21, -7, 7, 21}
Explanation:
The multiples of 7 are: 0, 7, 14, 21, 28, 35, ... both the positive and negative versions of each number. Erase the even numbers in that list to end up with 7, 21, 35, ...
Choice A fits the description, but there are items missing, namely -7 and 7. So this answer choice is crossed off the list
Choice B has both odd numbers and multiples of 7 listed. Every number is listed. This is why this is the answer.
Choice C has multiples of 7, but these are even numbers. We can cross it off the list.
Choice D is a similar story to choice C, though it has some odd numbers in this list.