Fillintheblanksinthefollowingseyenceswith"yet"or"till".
1HelearnedEnglishforthreeyearsatschool.___hedoesnotknowmuchaboutit.
2Mathematicsisnotverypopular;___onecanlearnalotinthecourse.
3Ididnotstarttolearnscience___becameamiddleschoolstudent.
4Theyworkedhardontheproblem___atlastthesolvedit.
5Thisclassisanelective;___mostoftheboyslikeitverymuch.
6Hereadthestory___helearneditbyheart.
理由。