英语语法：you are sad about not being invited 主要是介词后面的介词宾语不懂about not being invited为什么可以用being?动名词作介词宾语?invited又是怎么回事?什么时态?为什么invited又可以跟being?

Are you sad? Why are you sad? are you sad or angry? Where are you when I was sad never frown,even when you are sad Please don't sad you are Why are you crying (用sad回答) Who are you so sad?中文 Are you feel sad?和Are you feeling sad?有什么区别? if,you,are,are,sad,feeling,blue连词成句 You are sad,They aresad和We are sad有什么区别 What is the m__with you?why are you sad? Never frown,even when you are sad,because you ... who _______(给予)you help when you are sad. don't be so sad...you are the best one! never frown,even when you are sad.什么意思 What should your friend do if you are sad? Don't sad.You are a happy girl.改错