marik wrote:Which one of the following is correct ? and why are the others wrong ?

1. We propose that the school board disband. (i know this is correct coz of the subjunctive structure)
2. We propose that the school board be disband.
3. We propose that the school board should be disband.

Thanks in Advance.

I'm happy to help with this.

What is tricky about these is that the verb "to disband" can be used both transitively as well as intransitively --- that is to say, it can be used as a action a single body undertakes (e.g. "the school board disbands") or it can used as an action that one body performs upon another (e.g. "the mayor disbands the school board")

The first one is perfectly correct:
1) We propose that the school board disband.
Good use of the subjunctive!

The second two are incorrect, in part because you need the appropriate passive structure. Here are improved versions of those two:
2a) We propose that the school board be disbanded.
3b) We propose that the school board should be disbanded.

Version #2a is perfectly correct now. Version #3a is still wordier than needed, and therefore would not be correct on GMAT SC.

Here are a few blogs you may find relevant:
https://magoosh.com/gmat/2012/active-vs- ... -the-gmat/
https://magoosh.com/gmat/2012/gmat-gramm ... ive-tense/
https://magoosh.com/gmat/2012/gmat-sc-wordy-vs-concise/

Does all this make sense? Let me know if you have any further questions.

Mike