Which of the following is a poikilothermic animal?

The correct option is A Tortoise
A poikilotherm is an organism, whose internal temperature varies considerably. It varies with the temperature of its surroundings. Mammals and birds are homeotherms, therefore otter and whale being a mammal and penguin being a bird are homeotherms. Tortoise being a reptile is a poikilotherm. Hence, option A is the correct answer.