All following factors contributed to the drop of the resources-rich economies EXCEPT ______.

参考解析：

细节理解题。根据第五段第四句“A slowdown in Chinese commodity purchases played a part.”中国大宗商品采购放缓起到了一定的作用，可知A选项“降低了在中国的购买力”正确。根据第五段第三句“The first drop reflected a collapse in demand following the global financial crisis”可知B项正确；根据第五段倒数第三句“But in the case of oil, a rise in supply (and projected supply) was more important. The boom in tight oil and shale production in America prompted OPEC, the oil exporters’ cartel, to pump more crude to defend its market share”可知C项正确；根据第五段最后一句“Cheap energy, in turn, cut the cost of agricultural production and dampened demand for biofuels, leading to lower prices for grains and soybeans.”廉价能源降低了农业生产成本并抑制了对生物燃料的需求，导致谷物和大豆价格下降，可知C项虽然表述正确，但不是资源丰富的经济体的下降的原因，而是导致的结果。故选D。