from endless homework on weekends, the students now find their own activities, such as taking a ride together to watch the sunrise. A．Freed B．Freeing C．To free D．having freed 题目和参考答案——青夏教育精英家教网—

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____ from endless homework on weekends, the students now find their own activities, such as taking a ride together to watch the sunrise.

A．Freed B．Freeing C．To free D．having freed

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____ from endless homework on weekends, the students now find their own activities, such as taking a ride together to watch the sunwise.

A. Freed B. Freeing C. To free D. having freed

____ from endless homework on weekends, the students now find their own activities, such as taking a ride together to watch the sunwise.

A、Freed B、Freeing C、To free D、having freed

____ from endless homework on weekends, the students now find their own activities, such as taking a ride together to watch the sunrise.

A、Freed B、Freeing C、To free D、having freed

We learned that fossil fuels were formed before and during the time of the dinosaurs（恐龙）. We are using up the fuels. We can save fossil fuels by protecting and finding ways to use energy from “endless sources”, like the sun and the wind. Some people suggest that we should start using hydrogen（氢）.

Hydrogen is a colorless, smell-less gas that takes up 75 percent of the whole universe. Hydrogen is found on earth only in mixture with other elements such as oxygen, carbon and nitrogen. To use hydrogen, we must separate it from these other elements.

Hydrogen can be used in NASA’s space program as fuel for the spaceships, and in fuel cells that provide heat, electricity and drinking water for astronauts. Fuel cells are devices that directly change hydrogen into electricity. In the future, hydrogen could be used to fuel vehicles and aircraft and provide power for our homes and offices.

Hydrogen can be made from natural gas. An electrical current can also be used to separate water into its elements of oxygen and hydrogen. Some plants in the sea and bacteria（细菌） give off hydrogen through sunlight under certain conditions.

Hydrogen as a fuel is high in energy. Yet a machine that burns pure hydrogen produces almost zero pollution. NASA has used liquid hydrogen since the 1970s to drive rockets and spacecraft into orbit. Hydrogen fuel cells power the spacecraft’s electrical systems, producing clean by-product-pure water, which the crew drinks.

56. We can get hydrogen from the following EXCEPT ______ according to the passage.

A. natural gas B. water C. creature in the sea D. bacteria

57. Why could the hydrogen be used widely in the future?

A. Because it is of high quality.

B. Because it has no pollution.

C. Because it is easy to get it from all kinds of ways.

D. Because there are much hydrogen existing in the universe.

58. The passage mainly tells us ________.

A. the usage of a new energy source B. the future energy sources

C. a new energy source －hydrogen D. how to get the energy source

from endless homework on weekends, the stuclents now find their own activities to enjoy.

A．Freed

B．Freeing

C． To free

D．Having freed

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