题目

Wind power is a very clean source of energy. This is how wind power works. Wind makes windmills spin (旋转). When the windmills spin, they make electricity. Then we can use the electricity. A lot of people think that wind power is new, but that’s not true. For thousands of years, people have used wind to sail boats and move water. We still do those things today, but these days we mostly use wind power to make electricity. Wind power is a very popular source of energy. Most people think that we should use it more and more. First of all, it’s clean. Windmills don’t pollute the environmen下列等式：①， ②， ③，  ④⑤， ⑥；正确的有                               （    ）个． A.4          B.3           C.2           D.1