The reason (why/that) Peter hasn't come is that he didn't catch the train.
That Peter hasn't come is because he didn't catch the train.
He thinks it (is) important to prepare for / be prepared for every/each exam.
In his opinion/view, it matters/counts to be/get ready for every/each exam.
As far as he is concerned, it is of importance to make preparations for every/each exam.
解释1： 第一句话翻译时可采用这两个句型：1）The reason (why/that) ...is that...（why/that引导定语从句，reason后面的why或者that可以省略；that引导表语从句）; 2) That ...is because...(that引导主语从句，because引导表语从句）。catch the train赶火车。
解释2：他认为，以他之见可以用短语in his opinion/view, 或者as far as he is concerned 和he thinks。think it important=think it is important。be important = be of importance= matter/count ......很重要。prepare for...=be prepared for...= be/get ready for...=make preparations for...为......做准备。