简介:首先请看几个例句:a.IfIhaveseenfurtherthanmostmenitisbystandingontheshouldersofgiants.(IssacNewton)b.IfIamajanitoritiseitherbecauseIhavetobeajanitororIwanttobeajanitor.(J.A.Mcpherson,'GoldCoast',1968)c.ButifhewaseverhappyitwasinthesefirsttenyearsinVienna,whenhewasgraduallyestablishing