💡 Detailed Explanation
"難航" (nankou) means that something is encountering many obstacles and not progressing as expected. It is often used for situations like negotiations, meetings, or voyages that are not going smoothly. "交渉が難航する" (negotiations stall) is a common collocation. Other choices: "難関" (nankan) is a noun meaning a difficult barrier or hurdle and cannot be used as a verb here. "苦渋" (kujuu) refers to mental anguish or a difficult decision, describing a person's feelings rather than the state of the negotiations. "難渋" (nanjuu) also means to be stuck, but it's more often used for physical blockages like traffic jams.