1. It must have been a very arduous task to build the pyramids.
    当时建造金字塔肯定是件万分艰巨的事。

2.

2. He made an arduous effort to keep up with the rest of the class.
    他努力跟上班上其它同学。

1. arduous

1. 费劲的：alert 敏锐的;警惕的 | arduous 费劲的 | artistic 艺术的

2. 艰巨的; 努力的：arboreal 树木的; 树状的 | arduous 艰巨的; 努力的 | ascertain 查明, 确定

3. 艰巨的：Robust:强健的 | Arduous:艰巨的 | Gait:步态

4. 费力的：process 过程 | arduous 费力的 | admission 接收,录取

1. 困难的；艰巨的；费力的
    Something that is arduous is difficult and tiring, and involves a lot of effort.

    e.g. ...a long, hot and arduous journey...
           一段漫长、炎热而又艰苦的旅程
    e.g. The task was more arduous than he had calculated.
           这项任务比他所估计的要艰巨得多。