OPT: (I). weather energy; (II). geothermal energy; (III). solar energy; (IV). wind energy;

Answer the following question given this paragraph: 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. Q: What energy source, now making a comeback, has helped propel ships and pump water for many years? A:
Answer:
(IV).