The answer is A Have some volunteers drink nothing at all
Step-by-step explanation:
A control group is a group of people who don't have the variable they are the base and what we compare everything to so we would see if their mouth was spicy after eating it and not drinking anything then we would know that if someone drinks milk and their mouth is not spicy then it worked but if we don't have the control group then how do we know that just not drinking milk wouldn't have worked
Assume that the other number is y. we know that the addition of both number is -9 this means that: x+y=-9 reorder this equation to seperate the y variable: y=-9-x
