yet、while 都为“然而”时的区别

应该添 yet yet是‘然而在此基础上...’ while是比较两的东西，比如：I was watching tv, while Melissa was doing her homework. however用于转折，不是比较。用however的时候，前面诉说一件事的一方面+however+这件事的反面. 解释的不是太好。主要得靠感觉