SC - Searches

[mygmat800]

Roadblocks on major holidays, even if they are set up only to check drivers’ licenses and seat belts, are spontaneous searches of every driver, even the ones who have committed no crime. Without establishing probable cause, I believe such searches should be illegal.

A Without establishing probable cause, I believe such searches should be illegal
B Unless establishing probable cause, such searches, I believe, should be illegal
C I believe such searches should be illegal, without establishing probable cause
D I believe such searches should be illegal, unless officers have established probable cause
E I believe without establishing probable cause that such searches should be illegal

[Guest]

Between B and D, i chose B. Although B sounds wordy, I chose it over D because of that "," before unless in D. My question is - how do we decide whether to put a comma before a conjunction? (Of course in a list - before the last item we need a comma). Other cases?

[mygmat800]

Source: GMATClub Challenges