At the university, all matriculated students have been inoculated agai

why have been is correct? what's wrong with were?

As long as the intended meaning of the author is not clear, both A and B could be considered correct. This question does not seem to be from an authentic source.

Ideally it should be simple past as present perfect doesnt show any relation to the present action .

"inoculation'" happened at an unspecified time. Therefore, present perfect is the correct tense to use.

"Lask week, my friend watched the movie La La Land" - this sentence has time specified hence simple past is used.

"My friend has watched the movie La La Land" - this sentence doesn't have any time specified and hence present perfect is used.

That is how I will put my $0.02 on (A).

manhasnoname is right that we wouldn't use the present perfect with a time attribution, but that doesn't show why we use it here. Simple past can be used with or without a time attribution: "This morning, I ate waffles" or just "I ate waffles."

The reason we want present perfect here is that we are describing an accomplishment that extends into the present. We say "I have earned my Master's Degree" or "I have visited Asia" to show that this is something we have achieved. Sure, we can say these things in the simple past, but the connotation is not quite the same. In the case of this SC question, we are emphasizing that the work is done: the inoculations were completed for all students, and they still have that protection.

Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.