Advertisers have been using the principles of classical conditioning for years in attempts to associate pleasant feelings with their products. One particular genre of ads (for beer) is particularly famous for doing so by placing scantily clothed women holding beer bottles on large billboards. What are the unconditioned stimulus and the unconditioned response in this example

I believe we can say the unconditioned stimulus is the scantily clothed woman, while the unconditioned response is arousal.

Explanation:

In classical conditioning, unconditioned stimulus is one that triggers a response, a reaction, naturally, automatically. Unconditioned response is, of course, the natural reaction we show when presented with an unconditioned stimulus. It is an automatic, unlearned response, a reflex. In the situation described, the US is the scantily clothed woman in the ad who is holding a bottle. The UR it causes - at least in most heterosexual men - is arousal. The advertisers hope to create an association of the woman with the beer she is holding to condition the response of arousal when the beer is seen, motivating men to buy it.