She performed the most challenging task without a mistake.

她毫无差错地完成了这一有挑战性的任务。

The newspaper was directly challenging the government’s legitimacy.

报纸直接质疑政府的合法性。

The new play poses some challenging questions.

这出新戏提出了一些有挑战性的问题。

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

他的犹豫不决使他失去了一次得到新具有挑战性的工作的机会。

We have changed the course to make it more challenging.

我们改了课程以使其更具挑战性。

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，像合国员，像律师等。