when is adaptive radiation most likely to occur and for what reason
a- after a mass extinction , because the survivors give rise to species that fill new inches

b- just before a mass extinction , because species are competing intensely for limited resources

c- when the climate is warmest,because high temperatures act to increase the rate of evolutionary change

d- when the climate is stable , because a stable environment tends to decrease the rate of evolutionary change

Adaptive radiation is a phenomenon that refers to the process in which there occurs an enhanced diversity of organisms and old specie give rise to the evolution of a diverse array of new species.

The process of adaptive radiation can occur under special circumstances for example, when there occurs a change in environment in such a way that there are more environmental resources to sustain new organisms.

There is a famous example of Adaptive radiation that is finch speciation on the Galapagos that was well studied and researched by Darwin.

Here are the conditions under which adaptive radiation can occur:

A volcanic explosion has occured that opened up new habitats for the speciation. For example: The volcanic eruption in Hawaii that created an Island in middle of ocean.
Any event in which specie extinction occurred and and that open up new niches for the habitat formation and speciation.
If the newly created habitat is far off and isolated from an environmental which is populated. There are chances that new specie will colonize in that newly created habitat.
New habitat has enormous amount of resources to sustain the survival of diverse array of species.

In view of above facts, option A is best option.

Hope it help!