by基本解释

prep,通过；被；依据；经由；在附近；在……之前,同近

I was attacked by a dog..我被一条狗袭击。

通过；被；依据；经由；在附近；在……之前英释中释prepused especially with a passive verb to say who or what does something or makes something happen

by oneself,独自地，单独.短语