关于新概念第二册第42课的时态AswehadhadalongwalkthroughoneofthemarketsofOldDelhi,westoppedatasquaretohavearest.Afteratime,wenoticedasnake-charmerwithtwolargebasketsattheothersideofthesquare,sowewent

　　关于新概念第二册第42课的时态

　　AswehadhadalongwalkthroughoneofthemarketsofOldDelhi,westoppedatasquaretohavearest.Afteratime,wenoticedasnake-charmerwithtwolargebasketsattheothersideofthesquare,sowewenttohavealookathim.Assoonashesawus,hepickedupalongpipewhichwascoveredwithcoinsandopenedoneofthebaskets.Whenhebegantoplayatune,wehadourfirstglimpseofthesnake.Itroseoutofthebasketandbegantofollowthemovementsofthepipe.Wewereverymuchsurprisedwhenthesnakecharmersuddenlybegantoplayjazztunesandmodernpopsongs.Thesnake,however,continuedto'dance'slowly.ItobviouslycouldnottellthedifferencebetweenIndianmusicandjazz!

　　在第一句之外,文中很多句子中描述的动作是有前后的,为什么没有再用到过去完成时态?比如第二句“wenoticedasnake-charmerwithtwolargebasketsattheothersideofthesquare,sowewenttohavealookathim.”,noticed应该是在"wenttohavealookathime"之前发生的,即是在“过去的过去”发生的,为什么不用过去完成时?希望能逐句把时态讲解一下,