Are all yogurt probiotic ? if not...what makes them so (?)
No, the yogurt that are probiotic will be labeled. Activa brand was one of the first products available, now more and more mainstream companies offer yogurt with probiotics.
Not all yogurt are probiotic, and the bacteria in the yogurt is what makes it probiotic.
Nope, pasteurization kills bacteria. They have to add the probiotics (bacteria) afterwards to make yogurt probiotic.