(21)Miss, what time is flight 452 for Boston due to depart? 小姐,去波士顿的452次航班预定几时起飞? 虚词在句中一般不担任句子成分,其位置常常比较固定。冠词置于名词之前。如: (22)Karl bought a video recorder. 卡尔买了一台录像机。 介词一般置于名词或代词之前。如: 连词置于词与词、短语与短语、分句与分句、主句与从句之间,或置于从句之首。如: (28)Most students in the class score eighty percent and above ,but john is the exception. 班里大多数学生的考分都在80分或80分以上,但约翰却是例外。 (29)Henry is afraid he'll gain weight if he stops smoking. 亨利害怕不抽烟会发胖。