非谓语动词什么时候用不定式类?什么时候用v+ing形式?答:②当谓语动词begin,continue,start等是进行式时,如:Thestudents are starting to work on the di fficult maths problem. ③begin,continue,start与know,understand等状态动词连用时,如:I soon began to understand what was happening. ⒋advise,allow,encourage,forbid,permit等动词后接动名词作宾语,或带不定式作...