小题1:A
小题2:A
小题3:C
小题1:主旨大意题。结合文章的主题句第一段的why the roots of the plants always know which way to grow—into the soil but not above it? Some British scientists have recently solved this mystery可知答案。
小题2:细节理解题。结合A protein(蛋白质) at the tip of the root hairs called RHD2 helps them to take calcium(钙) from the soil. Calcium makes the hairs grow, and produce more RHD2, and take more calcium. 可知答案。
小题3:推理判断题。结合it will be some time before new cultivars(栽培变种) are developed. 可知答案。