在英语四级考试中，为了表达“加油”的意思，可以使用以下几种表达方式：

Make an extra effort to cheer sb. on

All aircraft must fuel before flight- 这句话比喻在考试前需要充分准备，积累知识和经验。

The machine wont function properly if you dont oil it well- 这句话比喻如果不努力准备，考试就不会顺利。

结合这些表达，你可以在四级考试中写下类似以下的句子来鼓励自己和他人：

"Let's make an extra effort to cheer each other on during the exam."

"Just like all aircraft need to fuel before flight, we need to prepare well before the exam."

"Remember, if we don't oil the machine well, it won't function properly. Let's do our best to prepare."

这些句子不仅传达了“加油”的意思，还带有一些鼓励和准备的元素，适合在考试前使用。