+0

The school........ exactly twenty years ago today.

a. was opened b. has opened

I go for "was opened". Is it OK to say "20 years ago today?

+0
Omar AhmedI go for "was opened".

Good. You can't use the present perfect with a specific mention of time.

Omar AhmedIs it OK to say "20 years ago today?

Yes. It's the same as "20 years ago to the day".

On October 23, 2021 you can say that October 23, 2011 was 20 years ago today.

CJ