Though most red tide outbreaks cannot be controlled, some can be prevented by A. Adding salt to ocean water.
B. lowering the temperature of coastal water.
C. reducing pollution in waters close to a coast.

B. It is a general idea about human nature.

Explanation:

Summary refers to a brief description of the main points. It is a precise outline of what is explained elaborately. The important points are noted and mentioned.

The theme refers to the subject or the main topic associated with the narrative. It can be presented in a line or two.

The given statement is a theme because it is a general idea that has been presented about human nature. It is not a brief description of an entire thought.