Q15: In parts of South America, vitamin-A deficiency is a serious health problem, especially among children. In one region, agriculturists are attempting to improve nutrition by encouraging farmers to plant a new variety of sweet potato called SPK004 that is rich in beta-carotene, which the body converts into vitamin A. The plan has good chances of success, since sweet potato is a staple of the region’s diet and agriculture, and the varieties currently grown contain little beta-carotene. Which of the following, if true, most strongly supports the prediction that the plan will succeed? - The growing conditions required by the varieties of sweet potato currently cultivated in the region are conditions in which SPK004 can flourish.
- The flesh of SPK004 differs from that of the currently cultivated sweet potatoes in color and texture, so traditional foods would look somewhat different when prepared from SPK004.
- There are no other varieties of sweet potato that are significantly richer in beta-carotene than SPK004 is.
- The varieties of sweet potato currently cultivated in the region contain some important nutrients that are lacking in SPK004.
- There are other vegetables currently grown in the region that contain more beta-carotene than the currently cultivated varieties of sweet potato do.
为什么是A呢?我怎么看C对啊. | 
