The students have been preparing/have prepared well for this event ...

[mohamido]

The students………. well for this event so it is getting everyone’s admiration.

a) have been preparing
b) have prepared

I think both of them are correct but the exam needs only one answer.

 

[teechar]

so it is getting everyone’s admiration.

This tells you that the event is occurring now, which means the preparation is over.
Can you guess the appropriate answer?
By the way, please do not use bold text unnecessarily. I edited your post to change it to plain text.

 

[Skrej]

I think both of them are correct but the exam needs only one answer.

Please tell us the source (including the author) of the text you're citing. What kind of exam is this?