在哲学辩论中，他那种复杂的推理思路让我完全跟不上了。

He lost me with his convoluted ___line ___of reasoning during the philosophy debate.

侦探决定追踪一条新的、有希望的调查线索。

The detective decided to pursue a promising new ___line ___of investigation.

她的论文探讨了一种关于可持续城市设计的非传统思路。

Her essay explores an unconventional ___line ___of thought on sustainable urban design.