Given a scientific passage and an answer, generate a question for the given answer.
--------
Question: Passage: The convection zone surrounds the radiative zone. In the convection zone, hot material from near the Sun's center rises. This material cools at the surface, and then plunges back downward. The material then receives more heat from the radiative zone. Answer: convection zone

Answer: Hot material from near the sun's center rises in which zone?

Question: Passage: solid waste that remains after food is digested and is eliminated from the body through the anus. Answer: solid

Answer: What type of waste is eliminated from the body through the anus?

Question: Passage: The whirring blades of these wind turbines look stark against the darkening sky at sunset. The energy of the wind causes the blades to spin, and the energy of the spinning blades is used to generate electricity. People have been using wind for energy for centuries. Until about 200 years ago, for example, ships depended on wind to sail the oceans. And windmills have long been used to gather wind energy to pump water and do other useful work. Today, wind energy is making a comeback. Do you know why? What might be advantages of using the wind for energy? This chapter has the answers. Answer: wind energy

Answer:
What energy source, now making a comeback, has helped propel ships and pump water for many years?