难题 /nántí/ angolul

challenge [challenges]▼(difficult task)
noun
[UK: ˈtʃæ.ləndʒ] [US: ˈtʃæ.ləndʒ]

problem [problems]▼(difficulty)
noun
[UK: ˈprɒ.bləm] [US: ˈprɑː.bləm]

puzzle [puzzles]▼(anything difficult to understand or make sense of)
noun
[UK: ˈpʌz.l̩] [US: ˈpʌz.l̩]