At the outset, it seemed necessary to be on guard against the other two.

一开始，似乎有必要提防另外两个。

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In the absence of a common goal or common enemy, they prefer to be on guard against each other.

在缺乏共同目标或共同敌人的情况下，他们宁愿相互防备。

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To be on guard against theft, the school has issued regulations specifying the duties of the door keepers.

为了防止盗窃，学校已经制定规章制度，明确规定了大楼看管员的职责。

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Investors: watch out for TICs no, not the bloodthirsty kind you have to be on guard for after a charming walk in the woods.

FORBES: TICs Suck Investors Dry

The nerve helps speed up the heart when it is necessary to be on guard and to calm the system down when we feel safe.

FORBES: Yes, You Can Think Your Way To A Better, Longer Life!

Many but not all ETF strategists use backtesting, and investors who are accustomed to mutual funds, where regulations generally forbid this practice, need to be on guard against it, experts say.

WSJ: When Cheap Funds Cost Too Much