这道数学题中最难理解的部分是隐藏的变量关系。

The ___trickiest part of this math problem is the hidden variable relationship.

这些问题是最难正确回答的。

These questions are the ___trickiest to answer correctly.

这个拼图游戏中最棘手的部分是最后几块拼图。

The ___trickiest part of this puzzle game is fitting the last few pieces.