We tend to think that anything more than a few years old must be hopelessly outdated.

我们往往会认为几年前的东西一定已经过时了。

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The book whose cover is very old must have been published a long time ago.

那本封面破旧的书肯定是很久以前出版的。

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The old must give place to the new.

老的必须让位于新的。

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They must be at least twenty-five years old, an American citizen for at least seven years and live in the state they represent.

VOA: special.2009.08.14

"I must call Mister Behrman up to be my model for my drawing of an old miner.

VOA: special.2009.08.01

Nominees for these academies must be seventeen to twenty-three years old, unmarried and with no children.

VOA: special.2009.06.04

Galica said the 31-year-old must ready for the physical challenge if she is to drive in F1.

CNN: Pit-lane pioneers: Women in Formula One

Tata Motors could also benefit, said Ramakrishnan, if a scrappage law under which vehicles over 15 years old must be replaced, is implemented.

FORBES: Magazine Article

For instance, a five-year-old must recognize different coins while a 13-year-old must create a budget, says Suzanne Harper, the Girl Scouts' director of program resources.

WSJ: Making Young Kids Smarter About Finance