Answer: C) the number of people who redeem the coupon.
Step-by-step explanation:
The coupon was for people who tried the makeup if they saw the ad. To measure how many people tried the new makeup then based on the ad it would be best to use the number of people who redeemed that coupon when purchasing because it would mean that those people saw the ad and decided to act on it especially if the ad contained an actual physical coupon or a digital coupon that can only be used once. This way Maybelline will know for a fact that those using the coupons saw the ad.