I believe the answer would be D in this case. since you don't for sure know the answer it wouldn't be A or C, and it's bad customer service to send a customer away without giving them full help therefore eliminating B. that leaves you with D
These substances are known as allergens, and when your body reacts to them, it causes an allergic reaction. You can inhale, eat, and touch allergens that cause a reaction. Doctors can also use allergens to diagnose allergies and can even inject them into your body as a form of treatment
