The correct option is D It is not necessary that oil prices would go down to earlier levels
Refer to the lines: The accepted wisdom is that we shouldn’t worry our little heads about that, because the incentives are there for business to build new production and refining capacity, which will effortlessly bring demand and supply back into balance and bring crude prices back to $25 a barrel. As Tommy Copper used to say, ‘just like that’. The key thing in this question is that you need to make an inference about the author’s view and not Tommy Cooper’s. The sarcasm in the author’s statement can be clearly seen and therefore, we can identify option (D) as the correct answer. Option (D) implies that the situation given in the extract above might not necessarily be correct.