This factory opened twent years ago同义句问题

This factory opened twenty years ago.这里,open 是动词
This factory has been open for twenty years.这里 open 是形容词,“开着的”
因为open作动词时,是瞬间动词,后面不能接表示一段时间的词组.所以,open 改为 be open (形容词),表示一个状态,后面就可以接for twenty years 这样一个表示时间延续的词组了.

has been open这里的open是形容词，并不是被动语态。
同义句应该改为This factory has been open for twenty years.
或This factory has been open since twenty years ago.
后面无论是for twenty years还是since twenty years ago都是表示一...

open在答案当中是形容词，be open是开着的状态。has been open 是现在完成时，强调从20年前就开一直开到现在。而不是你想的被动语态