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1·Police were on guard at Barnet town hall.

警察在巴尼特市政厅值守。《柯林斯英汉双解大词典》

2·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。

3·Two soldiers must be on guard all night.

两名战士必须通宵警戒。

4·But bid true knowledge stand on guard.

但要吩咐真知识看守着门口。

5·Two soldiers must be on guard all night.

必须有两个士兵整夜站岗。

6·The soldier who is on guard is my friend.

那个站岗的战士是我的朋友。

7·The world is alert and on guard as never before.

世界从没有向现在这样保持警惕和戒备。

8·All this time, the mother is constantly on guard.

在这段时间内，章鱼母亲一直在警戒状态。

9·On guard: Mexico City is at a virtual standstill.

站岗：墨西哥处在一个实际意义上的停滞状态中。

10·While danger threatens, we must all be on guard.

危险正在逼近，我们必须保持警惕。