The problem with this: Option b is not realistically an option. The whole point of Hamas hiding in civilian infrastructure and mingling with civilians is disguise. Or to put it another way: to make option b completely unfeasible. How would you identify Hamas members? Do they wear their bright orange terrorist uniform? Can you spot them by their mean facial expressions? And there is another problem with option b. Civilians in the building naturally do not see the IDF as their saviors from Hamas oppression, so there is a high chance that some of them will suddenly turn into non-civilians. Which leads to an out of control scenario and resulting bloodbath.
Disclaimer: This is not meant as a justification of option a. I’m just pointing out that option b is not a realistic option.