the medicine have an effect by the pain,为什么介词用BY?

the medicine have an effect by the pain,为什么介词用BY? The medicine has side effect.为什么? by the lake是湖边的意思吗?为什么要用by这个介词? what's the time ()your watch 为什么要用介词by by在这里的中文意思是什么? 英语翻译The "Bystander Apathy Effect" was first studied by resea He rent a house (by) the year.为什么括号内填介词by.“By+时间”的句子中不是要用过去完 “He had already posted the letter by five yesterday.”为什么要用介词 what's the time by your watch 为什么用by 为什么坐船用by sea不用by the sea I caught the thief by the arm.这一句中的by是什么意思?为什么用by呢? Have the effect on和Have an effect on有什么区别? (as) the time have gone by为什么不可用with