drop
1.drop可以用作“投寄（信件）”解，有“随意一投”的意思。例如：Please drop me a line. 和I dropped a note to him this morning.
2.drop in（偶然访问）后面接on或upon再接指人的词。例如：I dropped in (up) on him yesterday.
3.let drop（暗示，drop是不定式）后面有时接以that引导的从句。例如：Quite unexpectedly Paul let drop that he was thinking of leaving for Europe.
