TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: Deep currents are caused by differences in density at the top and bottom of the ocean.

SOLUTION: What is caused by differences in density at the top and bottom of the ocean?

PROBLEM: Hookworms infest the intestines.

SOLUTION: What part of the body do hookworms infest?

PROBLEM: Like all tetrapods except birds and mammals, frogs possess a heart with three chambers.

SOLUTION:
Like all tetrapods except birds and mammals, frogs possess a heart with what structure?