问一些高中的英语问题,请速速回答.
1.Hisgreatestworkwasdone_____hehadtheopportunityofmeetinganyofthegreatmenofphysicsofhisday.
A.afterB.beforeC.whenD.as
2.Alookofadisappointedcameintomymother'seyes___shereadtheletter.A.sinceB.becauseC.althoughD.as
3._____havinghadtenmonths'strictpractice,Idecidedtomakeonemoreeffort.A.WhenB.beforeC.AfterD.Until
4._____thedisscussionwasstillgoingon,thepresidentcameinandjoinedus.A.BecauseB.SinceC.WhileD.Before
5._____hehadapassionforwalking,westartedoffonfootinsteadofbycar.
A.WhenB.WhileC.AsD.After