Answer: B .

Explanation:
The volume of a cylinder is given by :_
, where r is radius and h is height of the cylinder.
Given : A new dolphin tank is being built outside of Houston. The tank will be a cylinder with a depth of 42 feet and a radius of 240 feet.
i.e. r=240 and h = 42
Now, the volume of tank will be :_

Hence, the tank will hold
water.