The door opened ______ (by itself / of itself). 究竟哪个正确?

题目

The door opened ______ (by itself / of itself). 究竟哪个正确?
of itself 自动的,
by itself 独自、单独；
for itself 亲自,为自己
以上为找到的参考资料,网络上存在两种答案,究竟是哪个呢?请专家详解,谢谢!

答案

by itself
by itself[英][bai itˈself] [美][baɪ ɪtˈsɛlf]
生词本
简明释义
独自地,无需外力地
How did the door open by itself?
门怎么自己开了?
《新英汉大辞典》
刚吃饭去了.是by itself.以上是资料来源.