【关于几道sat语法题1.Topersuadehisparentstolethimstudyabroad,Kennethdescribedotherstudents'positiveexperiences,(explainshowforeignstudywouldbenefithisfuturecareer,andassured)themthathecouldgetfinancialaid.括号里】

　　关于几道sat语法题

　　1.Topersuadehisparentstolethimstudyabroad,Kennethdescribedotherstudents'positiveexperiences,(explainshowforeignstudywouldbenefithisfuturecareer,andassured)themthathecouldgetfinancialaid.

　　括号里应该改为explainedhow..（后面一样）,为什么逗号能连三个动词啊?不是一个句子里只能有一个动词吗?

　　下面两题问括号里为什么错了,怎么改?

　　2.CubanmusicwassopopularintheColombiancityofCali(thusbecoming)thebasisforthedancescenethatpredominatedthreeduringthe1940s.

　　3.In1988aSovieticebreakingshiphelpedfreethreegraywhalesthathadbecometrappedintheArcticiceafterthey(hadswam)intothecoastalwatersofAlaskatofeed.