根据所给关键词，把下列句子翻译成英语

  1．在计算那道数学题时他们遇到了一些麻烦。(have difficulty in)

  2．我们热切盼望快点到达家乡。(look forward to)

  3．这位著名的科学家激动地说不出话来。(too…to…)

  4．他到这儿时，北京已发生了很大变化。(by the time)

  5．你应该给老师写信请两天假。(be supposed to)

1、1．They have some difficulties in working out the math problem．

2．We are looking forward to arriving in our hometown quickly．

3．The famous scientist was too excited to say a word．

4．By the time he came here，great changes had taken place in Beijing．

5．You are supposed to write to your teacher to ask for two days' leave.