1. She faced a knotty problem that required careful analysis.
她面对着一个需要仔细分析的复杂问题。
2. The new math concept is quite knotty for most students to understand.
新的数学概念对大多数学生来说非常难以理解。
3. The negotiation between the two countries reached a knotty stage.
两国之间的谈判进展到了一个棘手的阶段。