关于英语：为什么half past one不加a；而 a quarter past one要加aI need to explain.

关于英语：为什么half past one不加a；而 a quarter past one要加aI need to explain. 一道关于介词的英语题I go to sleep____ half past ten.A.in B.on C.at 请帮我翻译：Half past twelve Twenty to twelve Half past eleven Half past on until half past eleven on evening 问:let's make it(/)half past eight(on)the morning of June 21为什么half前不用 at half past seven为什么前面用at而不用on,in,to half past half past let's make it(/)half past eight(on)the morning of June 21为什么不用at,in? let's make it(/)half past eight(on)the morning of June 21为什么不用at,in? 改错my party is on half past five tomorrow Let's make it half past six.为什么half past six前面不加at 为什么7:30是half past seven.而不是at a half past seven 英语关于时间的用法,到底怎么用的 比如：half quarter past英语关于时间的用法,到底怎么用的 比如：half quarter past 除了这些还有哪些,在什么时候使用 求详解,不要复制, ---when do you usually go to bed at night?----at ( ) eleven.half past,a half past,half hour pasta half hour past,为什么选a It's half past five.希望英语高手们帮帮忙. 英语当中可以写half past seven o'clock吗? the party starts at half past ten 为什么加Sthe party starts at half past ten start为什么加S