Hello,

I'm having a hard time understanding why B is incorrect but A is. I chose B because it though it was implying that the children's preexisting condition made them more vulnerable to OPV than kids who don't have that. And I eliminated A because of the phrase "at least a few" because that sounds like a weak defense given they're only taking about "some"

So can someone please explain why B is wrong but A is right? Thank you