The first option describes a relationship between two abiotic (non-living) factors i.e. the effect of high temperature on the oxygen concentration of water.
Option 3 describes the relationship between two biotic (living) factors i.e. the smaller fish is prey for the larger fish.
Option 4 again describes the relationship between two abiotic factors i.e. the effect of increase in light on water temperature.
Therefore, the option 2 is the correct one as it describes relationship between tropical fish (biotic factor) and water temperature (abiotic factor)
I think the answer is {b.false} Infectious diseases are diseases that spread from one person to other either directly or indirectly. I think this is the answer.
