If something makes you sad when it ends.It must have been pretty wonderful when it was happening.From: William Hill 《This is US》《我们这一天》如果一件事结束时让你难过，那它发生的时候一定很美好。1. make sb/sth/yourself + adj 使变得，使成为The news made him very happ这则消息使他非常高兴。Can you make yourself understood in English.你能用英语表达你的意思吗？2. must have been ... 一定是。。。(对过去实事的推测)Your trip must have been fun.你这次旅行一定很开心吧。There must have been a pretty strong selective pressure.一定有很强的选择压力。It must have been very expensive moving such big trees.移动这么大的树一定很费钱。It must have been frightening, meeting strange men.你和陌生人见面，心里肯定很害怕吧。You must have done something right.你一定做对了什么事。