若5条鱼的平均质量为0.8kg,其中3条的质量分别为0.75kg,0.83kg和0.78kg，则其余2条的平均质量为_____kg.

属于知识密集型的高科技产业是()

you，me，please，could，help

______________________________________

隋朝时开通的大运河，其最南端在今天的()

JackisateacherofEnglish.Heisnotyoung，butheisnotold.Hehasaroundfaceandblackhair.Heistall.Therearefiftystudentsinhisclass.Theyalllikehim.Nowit'sintheafternoon.Look，somestudentsareworkingintheclassroom.Jackisthere，too.HeishelpingthemtostudyEnglish.Heisagoodteacher，andheisagoodfriendofthemall.

()1.WhatdoesJackdo?

A.Heisaworker.

B.Heisateacher.

C.Heisadoctor.

D.He'sanurse.

()2.Whatcolourishishair?

A.It'sblack.

B.Hisheiriswhite.

C.Itisbrown.

D.Hehasyellowhair.

()3.Howmanystudentsarethereinhisclass?

A.Therearefifteenstudentsinhisclass.

B.There'sfifty.

C.Hehasfifty.

D.There'refiftyinit.

()4.Jackisagoodteacher，isn'the?

A.Yes，heisn't.

B.No，heis.

C.Yes，he's.

D.Yes，heis.

()5.Whatarethestudentsdoingintheclassroom?

A.Theyarewalkingthere.

B.Theyaredoingtheirlessons.

C.Theyarehelpingtheirteacher.