Answer: option B. 4 feet above water.
Explanation:
This is an example of the use of the integer numbers.
Integer numbers are positive, zero and negative numbers.
In this case, zero is used to represent the surface of the water. So, any positive number will be the position above water and any netative number will be the position below water. That is why, while - 4 represents the position of the dolphin below water, 4 represents the position 4 feet above water.