为什么 three—hour 前要加“a”

为什么 three—hour 前要加“a” 我搞不懂了.It was （ ）journey.A three— hourB a three hour c a three—hourd three hour It is（three hours' drive ）from Shijiazhuang to Beijing.A.three—hours—drive B.three—hour drIt is（three hours' drive ）from Shijiazhuang to Beijing.A.three—hours—drive B.three—hour driveC.a three—hour driveD..a three—hour —driv It was _____journey.A three hour Ba three-hours C a three-hour Dthree hours It was a three-hour journey 中的hour为什么不加S,不是复数要加S的吗? Newcastle is ________ from London.A.a three-hour journey B.a three-hours journey C.a three hour journey It's three hours' drive from Beiijing to Shijiazhuang .three hours'drive同意短语A.a three- hour drive B three-hour drive -How far is it from Nanjing to Shanghai?-It's over_ A、three hour's drive B、three hours'drive C、three hours'drives D、three hour drive The students will have it finished in_.A.three quarters of an hour timeB.three quarters of an hour's it took us quite a long time to get to the military camp.It was__journey.为什么答案选“a three-hour为什么前面要加 a? The film is a three—hour documentary.(用last来改写句子,保持意思不变） Beijing is only drive from our hometown.A.three-hour B.three hours. Mr.Green will be back______ A.in three hour's time B.after three o'lock C.three hours laterMr.Green will be back______A.in three hour's time B.after three o'lock C.three hours later it took us quite a long time to get there.it was___journey.A.three-hour B.a three hourC.a three-hour D.three hours我想问一下时间怎么表示 It took us ----to finish this work.A .three hour and a half B.three and a half hour C. three and half hours D.three and a half hours 详细讲解一下 It's about ______ from here to there.A.three hours' drive B.three hour's drive C.three hours hours drive D.three hours drive It's about ( ) walk.A.three-hour B.three-hours C.three-hours' D.three-hours's给讲讲吧.谢谢! It is over _____from Shijiazhuang to Beijing.A.three hours’ drive B.three hour’s driveC.three hours’ drives D.three hours drive