challenge

A task or situation that tests one's abilities; something needing great mental or physical effort; a call to compete or dispute.

• challenging/ˈtʃælɪndʒɪŋ/(adj)有挑战性的
• challenger/ˈtʃælɪndʒə/(n)挑战者

• significant challenge
• face a challenge
• key challenge
• ongoing challenge
• rise to the challenge
• pose a challenge

1. 1.The biggest challenge is not the technology itself — it is changing the behaviour of the people who use it.
2. 2.She rose to every challenge placed in front of her, consistently delivering results in the most difficult circumstances.

• difficulty/ˈdɪfɪkəlti/— problem requiring effort
• obstacle/ˈɒbstəkəl/— something blocking progress
• hurdle/ˈhɜːdəl/— a difficulty to overcome

from Old French "chalenge" (accusation, dispute), from Latin "calumnia" (false accusation)