Answer:
A
Step-by-step explanation:
The correct answer would be the availability of krill.
A limiting factor is a substance or condition whose presence/absence can prevent a population from reaching its potential. Limiting factors can be biotic (living) or abiotic (non-living). Biotic factor includes the presence of competitive organisms in a population while abiotic factor includes food.
In the case of the blue whale, its diet is krill. Hence, its survival is largely dependent on the availability of krill. Otherwise, the blue whale might starve. Therefore, the availability of krill is a limiting factor for the population of whales.
The correct option is A.