D. is wrong because it is repeating a fact that is already present in the story: "existing varieties of sweet potato don't provide enough beta-carotene".
E. is correct because SPK004 would not be beneficial to the residents if it only improves beta-carotene but lacks another nutrient that is also as important. Solving one problem and creating another one is not feasible at all.
Hope this made sense.
-- by 会员 LR85 (2010/4/23 5:18:44)
文章讨论的是 种SPK004会不会成功,
所以D说的其他品种的甜土豆怎样怎样是和题目没有关系的。其他的品种我们根本不关系,我们关心的只是spk004好不好。
E对因为题目说甜土豆是主要产品,现在种的土豆不如spk004好,所以直接加强了spk004是成功的。
-- by 会员 rainbowmanutd (2010/4/22 23:30:18)