she is --------ing

she is --------ing where is she going?she后为什么用ing形式 she is ill now为什么不在ill后加ing buy(ing式）sing(ing式）she(宾格）five（序数词）is not（缩写形式） She is reading in the library中的“reading”要加ing 动词的第三人称都要加ing吗?就像we are having english class.she is reading this morning,she is going to the shops.这句话go为什么加ing? She is studying for the English test中studying 为什么要加ing She is always trying out new ideas ,为什么动词是ing形式? She is good at singsing(为什么sing加ing）?What abou am,is,are后的动词一定要ing吗?比如She is play,这句话就是错的吗? She is wearing a red dress这里的wear不是指状态吗 怎么有ING形式啊