The correct option is D Diapause - Zooplankton
Based on how an organism responds to the abiotic factors, they are categorised as regulators, conformers and partial regulators.
Conformers are organisms that are not capable of maintaing homeostasis. Thus in order to survive the unfavourable conditions, the conformers opt for alternative methods.
They either migrate to a place that provide favourable conditions or suspend their activities.
Hibernation, aestivation and diapause are classic cases of organisms suspending their activites during unfavourable condition.
During hibernation, organisms like bears, suspend their activities during winter. Whereas organisms like snails, suspend their activities during summer. This phenomenon is called aestivation or summer sleep.
Duration in which an organism suspends its development due to unfavourable conditions is called diapause. Certain species of zooplankton enter diapause during unfavourable condition. Thus option (a) is the correct pair.