She performed the most challenging task without a mistake.

她毫无差错地完成了这一最富有挑性任务。

The newspaper was directly challenging the government’s legitimacy.

报纸直接质疑政府合法性。

The new play poses some challenging questions.

这出新戏提出了一些富有挑性问题。

His indecision caused him to lose the chance of a new challenging job.

他犹豫不决使他失去了一次得到新具有挑性工作会。

We have changed the course to make it more challenging.

我们改了课程以使其更具挑性。

Take challenging composition courses (not just creative writing courses, but classes in journalism, technical writing, etc.) so that you can "speak" journalese, UNese, legalese, etc.

修习高级作文课程（不是创意写作课，而是像新闻写作，技术文件写作等等），这样才能说得像记者，像联合国员，像律师等。