题目解析:
插入句“In time, their efforts to transform the new countryside and make it more productive succeeded.”表明它的上一句应该说到人们在土地上的努力,下一句可能会对具体的成功进行描述,故选 D。前一句说到了 mapping , clearing , fencing , and planting wheat ,后一句 boasted of the newcomers’ achievements 。