1. reduce the relative clauses by a Present Participls (V-ing)
a,Students who arrive late will not be permitted to enter the classroom.
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b,The people who are waiting for the bus in the rain are getting wet.
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c,The scientists who are researching the causes of cancer are making progress.
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d,The helicopter which was flying toward the lake made a low droning sound.
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e,The man who is standing there is a clown.
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f, The envelop which lies on the table has no stamp on it.
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g,My grandmother, who is old and sick, never goes out of the house.