Why is E the right answer and not A?

In the United States proven oil reserves —the amount of oil considered extractable from known fields—are at the same level as they were ten years ago. Yet over this same period no new oil fields of any consequence have been discovered, and the annual consumption of domestically produced oil has increased.

Which one of the following, if true, best reconciles the discrepancy described above?

A) Over the past decade the annual consumption of imported oil has increased more rapidly than that of domestic oil in the United States.

E) Due to technological advances over the last decade, much oil previously considered unextractable is now considered extractable

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Can someone help me understand this logic? Why is D the right answer?

The theory of military deterrence was based on a simple psychological truth, that fear of retaliation makes a would-be aggressor nation hesitate before attacking and is often sufficient to deter it altogether from attacking. Clearly, then, to maintain military deterrence, a nation would have to be believed to have retaliatory power so great that a potential aggressor nation would have reason to think that it could not defend itself against such retaliation. If the statements above are true, which one of the following can be properly inferred?

A) A would-be aggressor nation can be deterred from attacking only if it has certain knowledge that it would be destroyed in retaliation by the country it attacks.

B) A nation will not attack another nation if it believes that its own retaliatory power surpasses that of the other nation.

C) One nation’s failing to attack another establishes that the nation that fails to attack believes that it could not withstand a retaliatory attack from the other nation.

D) it is in the interests of a nation that seeks deterrence and has unsurpassed military power to let potential aggressors against it become aware of its power of retaliatory attack.

E) Maintaining maximum deterrence from aggression by other nations requires that a nation maintain a retaliatory force greater than that of any other nation.

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