Which of the following biologic agents or diseases can be transmitted from person to person?

The correct choice regarding biologic agents or diseases that can be transmitted from person to person is influenza. Influenza is a contagious respiratory illness caused by influenza viruses that can spread easily from one person to another, primarily through respiratory droplets when an infected person coughs, sneezes, or talks. Additionally, it can be spread by touching surfaces contaminated with the virus and then touching one's face.

Ricin, on the other hand, is a potent toxin derived from the castor bean plant. While it can be lethal when ingested or inhaled, it is not transmitted from person to person.

Measles and tuberculosis are also communicable diseases. Measles spreads through respiratory droplets as well, and tuberculosis is primarily transmitted through airborne particles. Both of these diseases can be contagious in a manner similar to influenza, but the focus of the question likely emphasizes influenza as a more commonly recognized and widespread example of a person-to-person transmission agent in current discussions of communicable diseases.

In summary, influenza is a prime example of a contagious disease that individuals can easily transmit from one to another, which justifies its selection as the correct answer.