十三个难题 The Thirteen Problems

解决一个难题 solve a puzzle

一个难题 One difficult issue ; A difficult problem

处理这个难题 Deal with this problem

给我们出了一个难题 Give us a difficult question

幸福是个难题 Happiness Is a Problem

蜡笔小新-两个难题 Shinchan Double Trouble

真是个难题 It is really a problem ; Really a problem

这个问题很难解决 The problem defies solution ; defies solution