buck up：快活起来；振作起来

e.g. Come on, now, buck up. Things can't be all that bad.

行了，振作起来，情况没那么糟糕。

e.g. She began to buck up when I showed her the results of the tests.

当我给她看了考试成绩后，她又喜笑颜开了。

e.g. I know I have to buck up. Life must go on.

我知道必须振作起来。日子还得过下去。