Final answer:
The normal flora that are present only for short periods are referred to as transient. This contrasts with resident microbiota, which are always present.
Step-by-step explanation:
Normal flora referred to as transient are only present for short periods of time, now and then. The correct answer is a) Transient. Transient microbiota refers to microorganisms that are temporarily found in the human body, which may include pathogenic microorganisms. These transient organisms contrast with resident microbiota, which consist of microorganisms that constantly live in or on the body. Factors like hygiene and diet can influence the composition of both the resident and transient microbiota.