Correct Answer: Entomologist

Solution : The correct choice is the third option .

Entomologist is derived from entomon, which means insects, and logia, which means study. It is the study of insects and their relationship to humans, the environment, and other organisms.

The meanings of the other options are as follows:

• An activist is someone who tries to bring about political or social change.
• A cardiologist is a doctor who specialises in treating diseases of the heart.
• A naturalist is someone who observes the nature around us and has experience in all aspects of nature.

Therefore, entomologist is the correct one-word substitute for one who studies insect life .