Hiv is the virus that causes aids. in the mid-1990s, researchers discovered an enzyme in hiv called protease. once the enzyme's structure was known, researchers began looking for drugs that would fit into the active site and block it. if this strategy for stopping hiv infections were successful, it would be an example of what phenomenon?
a) vaccination
b) denaturation
c) allosteric regulation
d) competitive inhibition

The answer is; D

The drug will compete for the active site of the enzyme with the substrate hence is a competitive inhibitor. Increasing the level of the inhibitor reduces the chances that the substrate will bind the active site and this is how the drugs work. Vaccination involves introducing an attenuated form of the virus in the body so the body gains immunity against the antigens of the virus in preparation for a wild type virus infection.

he is very short, and he can only reach halfway up on the elevator buttons. but on a rainy day, he has his umbrella with him, and he uses it to poke the button at the top.

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link: