A “plus” sign in front of the number means you are farsighted， and a “minus” sign means you are nearsighted. These numbers represent diopters， the unit used to measure the correction， or focusing power， of the lens your eye requires. Diopter is often abbreviated “D”.比如某酒100毫升中纯乙醇含量为10毫升，这种酒的酒度就是10度。
例:By the time the fire engines got there， the whole building was already alight. 等消防车到那里时，整栋大楼都已经燃着了。
考研英语大纲词汇5500C-Dcab［kæb］n.出租车；驾驶室；轻便马车cabbage［ˈkæbɪdʒ］n.卷心菜，洋白菜cabin［ˈkæbɪn］n.小木屋；机舱，船舱cabinet［ˈkæbɪnɪt］n.内阁；贮藏橱，陈列柜cable［ˈkeɪbl］n.
