In these options listed below, we need to find a specific response to the question.

In Option A - INCORRECT, the option is not an appropriate response to the question. It's a repetition of the earlier statement underlined and the use of emphasis in the form of ''economical.''

In Option B - INCORRECT because the statement is a bit faulty due to the use of "an" with the "economic". It should have been less ambiguous.

In Option C - INCORRECT, It has the same problem of overemphasizing the "economical" part which is the reason why we won't pick it as a correct one.

In Option D - CORRECT, this is a simple and concise statement with a correct sentence formation devoid of much emphasis. "an" is better in usage with economic than economical in this context.

In Option E - INCORRECT, the use of the demonstrative pronoun that means a particular noun have been previously talk about and it's being replaced. In which case, it remains speculative.