单选题 Which of the following hypothetical discoveries, if made, would be most likely to reduce the technical difficulties in producing plastic from organic crops?

• (A) a source of refining fossil fuels that significantly reduces their cost to plastic manufacturers
• (B) a way of maintaining grain yields while producing high quantities of plastic that do not interfere with the functioning of plant chloroplasts
• (C) a means of reducing the clean-up cost of environmental damage wrought by CO₂ and SO₂ emissions
• (D) a means of yielding greater efficiency from coal-based fuels used in the organic plastic-production process
• (E) the discovery of a renewable source of plant-sugar that would lessen reliance on fossil fuels in organic plastic-manufacture