The argument against heating the formula in a microwave is that, because microwaves heat liquids unevenly, resulting hot pockets could endanger the baby. However this argument assumes that the state in which the liquid is removed from the microwave is the same state in which the liquid will be given to the baby. If the parent does something to alter the potential hot pockets between the microwave and the baby, then this presupposition would not hold. Answer choice D addresses this nicely, because it presents a way that parents could alter the state and thus eliminate the danger, and correctly demonstrates that this argument presupposes that the parents will not do this.

Answer choice A is out of scope, because it does not address the premise made in the argument about safety (rather brings up another point that is irrelevant to this argument). B is likewise out of scope, as the argument is not focused on health alterations to the formula, but rather just danger related to heat. C is focused on the correct topic of heat, but the variance among microwaves is not relevant and not necessarily presupposed here...even if all microwaves have the exact same power, this danger could still be a concern. E is out of scope for reasons similar to B.

I hope this helps!