Your friend's mother was always baking ginger-flavored cookies whenever you were at their house. you loved those cookies, and would eat several each time you visited one day. you noticed that you started to salivate as you walked up the front steps to the house, before you smelled the cookies the reason for this is that the house has become a(n):
a) unconditioned stimulus
b) conditioned response
c) unconditioned response
d) conditioned stimulus

Option B, Conditioned stimulus

Explanation:

Conditioned stimulus is a stimulus that gets associated with a non neutral act .

Here, if  salvation had taken place after smelling the food then it would have been an Unconditioned stimulus. But here "walking towards the front step" is an act that got associated with the salvation act which is a conditioned response .

Here a famous case of dog , food and bell can be seen for a better understanding.

a) Unconditioned stimulus - Smell of delicious food

Unconditioned response - salvation of dog

b) Now if a dog while feeding is made to hear some bell sound, then in near by future if he ever listens that bell sounds (Conditioned stimulus) he will associate it with food and ultimately will start salivating  (Conditioned response)

if you know your abc's you should be able to get your answer or just use google