—No, you needn't. (must (not)/ may(not) /can(not))

—No, you. My dad is sleeping. (must (not)/ may(not) /can(not))

—No, you__________. You may go home now, but you__________ go to the net-bar.

—It__________ be him. He has gone to Hong Kong.

—I clean the blackboard now?

—Yes, you. /No, you. No, you .

    Do you know the way of using wind power to make electricity? There are many advantages (优点) of using wind to make electricity. Here're some of them.

    First, it may be one of the cheapest ways to make electricity. Second, it can make and store hydrogen gas (氢气). The most important one is that it won't pollute the environment. Besides, the wind power can be reused.

    But large wind farms might kill birds too, because the birds always fly into the wind turbine (风力涡轮机). Scientists are looking for ways to stop them.

    Experts said that by the middle of the 21st century wind power could supply (供应) more than 10% of the world's electricity. The wind really helps us a lot.