________ are the animals in the cage given food? Once a day.

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I first met Lisa three years ago, she ________ at a radio shop at the time.

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The problem is ________ difficult that I can't work it out.

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________ endangered animals is very important to us.

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Something is wrong with my radio. It needs ________.

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We had to walk home, as the last bus ________.

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There are hardly people in the forest, ________?

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The doctor asked me to take the medicine ________.

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If rivers ________ with waste from factories, we'll die.

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A．polluted　　B．are polluted　　C．were polluted

After a break, they went on ________ their work.

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A．with　　B．/　　C．towards