这对我们所有人来说都是一段充满挑战的时期。

This has been a ___challenging time for us all.

像骑士一样，我们骑马穿越全国，寻找冒险和富有挑战性的活动。

Like cavaliers we ride across the country looking for adventures and ___challenging activities.

解决谜题可能非常有挑战性。

Solving puzzles can be very ___challenging.