How airplanes fly?

People {#blank#}1{#/blank#} (try) for a long time before they invented a {#blank#}2{#/blank#} (success) "flying machine". Now there {#blank#}3{#/blank#} (be) so many {#blank#}4{#/blank#} (plane) in the sky.

    An airplane {#blank#}5{#/blank#} (fly) because of the upward force(力量) of {#blank#}6{#/blank#} (move) air against its wings(翼). To get that moving air, it needs something {#blank#}7{#/blank#} (push) it forward—like a motor-driven propeller(螺旋桨) or a jet engine(喷气发动机). You can fly a kite if there  {#blank#}8{#/blank#} (be) enough wind to hold it up. An airplane is like a kite with such force!

    More and {#blank#}9{#/blank#} (many) young people are getting to like making model planes now. How about you? Are you interested in it after {#blank#}10{#/blank#} (read) this article?

—Yes. We should pay attention to the safety all the time.

—You'd better ask her to stop working and go to see a doctor.

— Yes, but only _______.

—I think she is old enough to take care of herself.