Even in this age of conservation, cooking ranges that consume fossil fuels are far more common than those that rely on magnetic resonance,
producing heat more efficiently than natural gas.
A. producing heat more efficiently than natural gas
B. producing heat more efficiently than natural gas does
C. which produce heat more efficiently than natural gas
D. which produce heat more efficiently than natural gas does
E. much more efficient at producing heat than natural gas
Option B: There seems to be a misconception about what is the real previous clause that the comma + verbing modifier is modifying. It is not the clause starting with the cooking ranges that consume fossil fuels (incidentally. natural gas is one such fossil fuel), but the relative clause that starts with the demonstrative pronoun -- 'those' that rely on MR. -- Therefore, it is clear that 'producing heat more efficiently than natural gas does" is justly modifying the MR based cooking ranges.
We can see that essentially, there are two comparisons involved in this hard nut of the question.
The first is the comparison between the cooking ranges of fossil fuels and the MRs. The first "than" marks this comparison.
The second one is about which produces heat more efficiently, whether NG or MR. The second 'than' signifies this aspect.
Both the comparisons should be dealt with one-on-one, like A vs. B and C vs. D but not A vs.C and B vs. D.