This is useful information. Presumably a lower burning cost is one of the advantages of low-wattage bulbs, but the degree of difference matters when we're comparing against the higher purchase cost. If low-wattage bulbs only cost slightly less to burn, then that weakens the argument by reducing the benefits. On the other hand, if the burning cost is much lower, that strengthens by increasing the benefits.

The argument is concerned with the cost-benefit of low-wattage bulbs to homeowners, so the benefits to the home lighting industry just aren't relevant. Regardless of how profitable these bulbs are, that doesn't affect how much they cost homeowners, or their benefits to homeowners. Because this is irrelevant, that makes it the correct answer: it's not useful in evaluating.

This is useful information, because the difference in purchase cost is the "cost" that may or may not be outweighed by benefits. If low-wattage bulbs cost much more to buy, then that may outweigh the advantages of low-wattage bulbs and weaken the author’s argument. If they only cost a little more, then the advantages likely outweigh the price difference, which would strengthen.

This is useful information, because it has the potential to add a cost or a benefit. If current users find low-wattage bulbs to be less effective than normal bulbs, then that would weaken by adding another cost that must be outweighed by the "enormous advantages." If homehowners find these bulbs extremely effective compared to normal bulbs, then that's an extra advantage, which would strengthen.

This is useful information, because like (D), it has the potential to add a cost or a benefit. If low-wattage bulbs last a significantly shorter time than normal bulbs, that adds a cost, which weakens the argument that we should all use low-wattage bulbs. If low-wattage bulbs last even longer than normal bulbs, that would be an advantage that would support the author's claim.