You Are Conducting an Experiment in Which You Are Trying

You are conducting an experiment in which you are trying to manipulate the immune response of rats by using the principles of classical conditioning. First, for several days of an experiment, you give rats artificially sweetened water with an immune system-enhancing drug in it. You later remove the drug and notice that the immune systems of rats are boosted when they consume the sweetened water. In your experiment, what is the unconditioned response (UCR) ?

A) The sweetened water
B) The drug
C) The enhanced immune system functioning in response to the drug
D) The enhanced immune system functioning in response to the sweetened water