求助几道单选题+讲解1.____modeling business is by no means easy to get

求助几道单选题+讲解
1.____modeling business is by no means easy to get into,the good model will always be in demand.
A.While B.Since C.As D.If
2.It was evening____ we reached the little town of Winchester.
A.that b.until C.since D.before
3.—You haven't lost the ticket,have you?
—___.I know it's not easy to get another one at the moment.
A.I hope not.B.Yes,I have C.I hope so D.Yes,I'm afaid so
4.Sientists think that the continents____always where they ____today.
A.aren't;are B.aren't;were c.weren't;are D.weren';were
答案是ADAC