Frankly this is a crazy question if you've never encountered its logic before but I thought on this for a while and I think i get it now. Here's my simple thought process:

Team1 (me) - 30% chance of winning

Team 2 - 25%

Team 3 - 20%

Team 4 - 15%

Team 5 - 10%

Among these, I have the highest chance of winning at 30% BUT my odds of defeat are the other 70% so with that in mind I am not more likely to win than lose.

The prompt says "almost certainly" and 70% chance of defeat is not certainty.

my thought process for selecting A was: The argument is citing 'cases of polio' as a reason for why we should switch. But if IPV creates new cases not only is it causing polio cases, it is also causing NEW ones, something OPV doesn't (as evidenced in the first sentence) so this would undermine the reason to switch.