an open / a closed book

an open book – 一本找天的书。一本打开的书，人人可读，书中的内容尽可一览无遗，因而没有神秘或言。这样的一本书便就用来比喻坦诚的人或公开的事，这样的人或事清澈如水，毫无不可思议之处。与此截然相反的是a closed book或a sealed book – 一本合起来的书，它意味着神秘和未知：

The dense dark jungle, obviously a closed book to an outsider, is an open book to the aboriginals.
黑暗稠密的丛林，对外来者显然是神秘莫测的，但对土著来说却毫无神秘可言。

The origin of the universe is still a sealed book to us.
宇宙的起源对我们来说仍然是不可知的。

My life experience has been very simple. It is an open book to every colleague of mine.
我的生活经历很简单，我的每一位同事都十分清楚。

last straw that breaks the camel’s back

这个成语似乎长了些，这是一个带有定语从句作修饰语的名词短语，直译为“把骆驼的背压坍的最后一根稻草”。骆驼素以其忍耐力著称，它可以许多天不吃不喝，驮着重物在一望无际的沙漠中行走。但凡事都有个限度，骆驼的负载能力也是如此，即使它的背能背负很重的东西，但一旦到了极限，那怕再加一根稻草也可以把它压垮。在生活中，也不乏我们的体力或精神的负担到达极限的情况，这时，那怕是再加一点儿负担，也足以导致全面崩溃：

Mary had a bad day yesterday. She missed the bus and was late for class. She quarreled with her neighbour, and then lost her glasses. When the teacher asked her to stay after school, it was the last straw that broke the camel’s back: she broke into tears.
昨天玛丽一天都不顺利，她误了汽车，上课迟到，她和邻座的同学吵架，又丢失了眼镜，当老师叫她课后留下时，她再也受不了了，哭了起来。

For the past few months, father has been overworking, doing all sorts of extra jobs, and the organization of the conference which he was asked to take care of last week was the last straw that broke the camel’s back: he had a stroke and was hospitalized.
过去几个月中，父亲劳累过度，他的额外事太多了，上周叫他负责组织一次会议，终于使他累跨了，他患脑溢血而住院了。