When an ad suggests that everyone except for you is using the product, they are using the _ _ technique.
a. put down
c. bandwagon
b. hidden fears
d. testimonial

They are using the bandwagon technique - C. 

If they used customer testimonials about how certain customers liked this product and you could see their actual testimonials, then D would be the answer. However, given the fact that the ad suggests that everyone uses this product except you, they're relying on the bandwagon technique. 

I’m pretty sure it’s 4, you can check on the calculator