do you have to go back_____5 o'clock?用by还是用at?为什么?请解释.

do you have to go back_____5 o'clock?用by还是用at?为什么?请解释. --Must I come at four o'clock? --用No,you don't have to.还是No, have to be home by 10 o'clock 为什么用by --May I come at four o'clock?--用No,you don't have to.还是No,I I have to be home by ten o'clock.为什么不是be at home? "I go to bed at about 11 o'clock.句中为什么用"about"? 补全对话：I go to school at seven o'clock.Do you also go to schoo ()()do you have dinner?At 6 o'clock. it's eleven o'clock.you have to go My two sons have to go to school at seven o'clock every day对 seven,night,get,at,have,i,home,by,o'clock,to seven,night,get,at,have,I,home,by,o'clock,to 英语连句