Choose the best answer to complete each sentence.

The machine works according to the                  of electromagnetic conduction.

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A digital camera is used for _____ the pictures and video clips in electronic format instead of to film.

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Up to now, the discount ______  to children under ten years old.

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They often use a webcam _____ moving pictures and sounds and allowing these to be broadcast on the Internet.

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We ______ in Hanoi for a long time.

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The Tower Infinity in South Korea is supposed to be the world’s first skyscraper that, for a few hours a day, _______ an unobstructed view of the sky behind it.

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None of the students ______ to class yet.