[Grammar] As to the preference of the use of article “the”

[Solutio]

Of the examples given below, why change is required in the use of article “the” before fans ? Is that really necessary ?
(https://www.grammar-quizzes.com/sent-cleft.html)

It was at the moment when the fans jumped on the stage that the band was surprised.
It was surprising that fans were jumping on the stage
On the stage was where the fans were jumping.
Fans jumping on the stage was what was surprising to the band

 

[Charlie Bernstein]

Of the examples given below, why is a change required in the use of the article “the” before fans[no space]? Is that really necessary[no space]?
(https://www.grammar-quizzes.com/sent-cleft.html)

It was at the moment when the fans jumped on the stage that the band was surprised.
It was surprising that fans were jumping on the stage
On the stage was where the fans were jumping.
Fans jumping on the stage was what was surprising to the band

That's an interesting question.

All four would be correct either way.

The difference is that "the" means it was all of the fans. Without the, it means some of the fans. (More information could change the context and the meaning.)