A person infected with an STI can pass the infection to another individual without knowing it because of which of the following?

a. The person is an active carrier.
b. The person is an asymptomatic carrier.
c. The person is an intermediate host.
d. The person a definitive host
e. The person is a passive carrier.

I think either a or b?

You could have found this information from the Internet:

Active carrier: a person without signs or symptoms of an infectious disease who carries the causal microorganisms and can transmit the disease to others.

Asymptomatic carriers are people who do not show any signs or symptoms of the disease on contracting it for the entire duration of the incubation period. This can last for around 14 days. As a result, they end up transmitting the virus to a lot of people.

A passive carrier is contaminated with the pathogen and can mechanically transmit it to another host; however, a passive carrier is not infected. For example, a health-care professional who fails to wash his hands after seeing a patient harboring an infectious agent could become a passive carrier, transmitting the pathogen to another patient who becomes infected.

Intermediate host is an organism that supports the immature or nonreproductive forms of a parasite.

Definitive host is an organism which supports the adult or sexually reproductive form of a parasite.