哈佛取得了领先地位，经过再三挑战后仍然镇定自若。

Harvard took the lead and remained unperturbed by the repeated challenges.

《柯林斯英汉双解大词典》

在不愿意牺牲自己个人安全的情况下，洛基挑战他们，做出的宝物是跟他的三项宝物相同的。

Loki challenged them to make treasures equal to the three he had, not being willing to risk his personal safety.

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迄今为止，解释睡眠和营养间的因果关系仍是一个挑战。可能存在第三个因素影响这两者。

It's as yet a challenge to explain the cause-and-effect relationship between sleep and nutrition. There may be a third factor that impacts both of them.

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