14.a hard nut to crack or a tough nut to crack<非正式>(difficult to understand)难题；难事；难点
Getting out there is in many ways the hardest nut to crack.从很多方面来说, 到那里去是最困难的事了。
15.nuts and bolts
(practical aspects)实质性内容；具体内容
He's more concerned about the nuts and bolts of location work.他更关心的是选址工作的具体内容。
16.off your nut<俚>(mad)疯狂的；狂热的；发疯的；愚蠢的