定义：

　　fail to understand, net get a clear idea of

　　不明白，得不到清晰的概念

　　例句：

　　The homework problems were so complex that all but the most brilliant students couldn't make heads or tails of them.

　　作业中的问题是那么复杂，除了非常聪明的学生外，都茫无头绪。