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He ______  off  alone a month ago, and _______ of since then.

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None of the students ______ to class yet.

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I can’t believe that you ______all the three exercises. You just started five minutes ago.

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

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A smart watch is used _____ you access to lots of information besides the time of day, such as missed calls, messages, and emails.

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We ______ in Hanoi for a long time.

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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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Tom often watches TV after his parents ______ to bed.

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Lima Billboard in Peru is used _____  clean water from Lima’s extremely humid air.

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“Where’s Tony?” “He ______ to the travel agent, and he hasn’t come back.”

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I’d like to see that football match because I ______one this year.

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Their children ______  lots of new friends since they ______  to that town.

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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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People use a tooth sensor ____  any bacteria causing cavities, or any other infections in your teeth.