--- Is your mother the same age ________ your father?

--- No, my mother is ________ younger than my father.

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The boy ________ back until his father called him.

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They said goodbye ________ me ________ the airport. They said, “Good luck ________ your trip!”

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People find ________ very important to develop the students' abilities.

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It's not easy ________ sorry to your best friends.

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My sister is ________ to go to school this year.

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My best friend is very worried because he has ________ money to ________ the summer camp.

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When you are ________ trouble. You should ask the policeman ________ help.

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You can't borrow colour pencils ________ Li Lei, because he doesn't have colour pencils, ________.

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--- Why is your sister upset?

--- Because she ________ the final exam.

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