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| afield (谱); aporia; conundrum; dilemma; floorer; Gordian knot; puzzler; quandary; spinosity; sticker; stickler; stumper; teaser; toughie; toughy | |||
| problem | |||
| crux | |||
| difficult problem; hard nut; staggerer | |||
| troublesome problem | |||
| challenge | |||
| hard nut to crack | |||
| roadblock | |||
| staggering problem | |||
| bottleneck | |||
| knotty problem; thorny problem; thorny subject | |||
| hot potato; puzzle; quiz | |||
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| tickler; twister; twistor | |||
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| poser | |||
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| crux | |||
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| quaestio vexata | |||
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| knot | |||
| 难题: 71 phrases in 22 subjects |