Answer and Explanation:
A) Unconditioned Stimulus- The onion
B) Unconditional Response- Crying
C) Conditioned Stimulus- Chiming clock
D) Conditioned Response- Crying
In the above scenario( an example of classical conditioning), Elmer has been conditioned by the continuous iterations of having to cook everyday by 5pm. He cooks with onions by 5pm around the same time his uncle's clock chimes five times. He cries/has teary eyes(unconditioned response) because of the response to the onions(unconditioned stimulus) around the same time the clock chimes five times thereby conditioning his response so that even when the onions isn't there/he isn't even cooking, he tears up to the clock chimes around 5pm. The clock is therefore a conditioned stimulus and there is a conditioned response of crying.
The unconditioned response to an unconditioned stimulus happens naturally(an instinct) because it is a biological response to the onions, not conditioned.