Most young children put their hands over their ears when they hear the loud boom of firecrackers at a Fourth of July festival, but at first pay scant attention to the person lighting the firecrackers

However, after just a few firecrackers have been exploded, some of the children put their hands over their ears as soon as they see the person approach the firecracker with a match! What is the unconditioned response?
a. the person lighting the firecrackers
b. the loud booming sound made by the firecrackers
c. the children putting their hands over their ears when they see the person about to light the firecrackers
d. the children putting their hands over their ears when the firecrackers explode

d