Can someone help what is this? Pls

Explanation:

Agent originally referred to an infectious microorganism or pathogen: a virus, bacterium, parasite, or other microbe. Generally, the agent must be present for disease to occur; however, presence of that agent alone is not always sufficient to cause disease.

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

d.

hope to be marked brainliest