positive: "12PM 是中午<br>记得我刚来美国的时候,有门课程12PM开始。当时我问教授怎么晚上那么晚了还上课。他笑着说12PM是中午。<br>其实,中国人中分不清楚12AM和12PM的大有人在。我相信很多人把12AM当成是中午,12PM当成晚上。就168肯定就有很多人分不清楚。<br>规则参看:钱多多选股大赛规则截止日期: 11/15/2009 12:00am EST.<br>报名截止。<br>所以我在规则里面,尽量不用12,都用11:59啥的。<br>Are noon and midnight 12 a.m. or 12 p.m.?<br>This is a tricky question. The answer is that the terms 12 a.m. and 12 p.m. are wrong and should not be used.<br>To illustrate this, consider that ""a.m"" and ""p.m."" are abbreviations for ""ante meridiem"" and ""post meridiem."" They mean ""before noon"" and ""after noon,"" respectively. Noon is neither before or after noon; it is simply noon. Therefore, neither the ""a.m."" nor ""p.m."" designation is correct. On the other hand, midnight is both 12 hours before noon and 12 hours after noon. Therefore, either 12 a.m. or 12 p.m. could work as a designation for midnight, but both would be ambiguous as to the date intended.<br>When a specific date is important, and when we can use a 24-hour clock, we prefer to designate that moment not"
negative: 1、不能,没有办法降级恢复以前系统了。苹果手机是不支持降级的,除非手机是iphone4,且事先备份了shsh。<br>2、苹果产品所有的固件安装都需要和苹果服务器验证,只有苹果服务器允许使用本固件,用户才可以使用,乔布斯曾经说过一句话,即软件与硬件是一体的,这也是苹果公司从来没有把自己的平台软件像windows或安卓系统一样随便授权他人使用(可参考乔布斯传)。<br>3、对于无法降级的说明:“为了防止设备被降级至缺乏最新安全更新的软件版本, iOS 使用了一种名为系统软件授权的流程。如果允许降级, 能够以物理形式接触到设备的攻击者将可以安装早期版本的 iOS, 并利用已在新版 iOS 中被修正的安全弱点”。— 摘自《iOS 安全白皮书》。