Acommensal bacterium
a) always causes disease in its host.
b) may also be an opportunistic pathogen.
c) is beneficial to its host.
d) isn't capable of causing disease in its host.
e) does not receive any benefit from its host.

The correct option is: b) may also be an opportunistic pathogen

Explanation:

Commensalism is a kind of symbiotic relationship between two different biological organisms. In this interaction, one of the organism is benefited whereas the other organism is neither harmed nor benefited.

The organism that gains benefits from the host is known as the commensal. The commensal may obtain benefits like shelter, nutrients, protection, and locomotion.

However, the commensal bacteria can be an opportunistic pathogen.

Opportunistic pathogens are the pathogens that can cause an infection or a disease if the host has a weak immune system.

answer: - few nutrients

high pressure

low temperatures

explanation: 1. few nutrients:   open-ocean zone is located way far from the land, which is the main source of the essential nutrients.2. high pressure: pressure increases by 1 atmosphere for every 10 meters increase in depth.3. ample sunlight: a large fraction of the sunlight is reflected back to the atmosphere from the sea surface. 4. varying salinity: below the thermocline, the water is isolated from the atmosphere so the salinity remains stable over the year.5. low temperatures:   the temperature of open-ocean zone ranges from a low of -2°c to an average of 17°c