修理这辆旧自行车很棘手，因为有些零件已经不再生产了。

Fixing this old bike is ___tricky because some parts are no longer made.

处理这项新工作中的伦理问题可能会很棘手。

Navigating the ethical questions in this new job can be ___tricky.

谈判的最后阶段是最棘手的。

The final stage of the negotiation is the most ___tricky.