I have to be home by 10 o'clock(对10 o'clock 提问）

I have to be home by 10 o'clock(对10 o'clock 提问） I have to be in bed (by ten o'clock).对括号内的提问 have to be home by 10 o'clock 为什么用by I have to be home by ten o'clock.为什么不是be at home? I have to be in bed by ten o'clock. I have to be in bed by ten o'clock.[用in bed提问] I go to school at seven o'clock.（对at seven o'clock 提问） We will get to Beijing at 10 o'clock.对(at 10 o'clock)提问 I have to get up at seven o' clock .对划线部分提问at seven o' clock I'm supposed to be at home by ten o'clock at night. I'm supposed him to be at home by ten o'clock at night.什么意思? seven,night,get,at,have,i,home,by,o'clock,to