题目选项分析

Developed by Pennsylvania's Palatine Germans about 1750, they made Conestoga wagons, which had high wheels capable of crossing rutted roads, muddy flats, and the nonroads of the prairie, and floors curved upward on their ends so that they prevented cargo from shifting on steep grades.

Developed by Pennsylvania's Palatine Germans about 1750, Conestoga wagons had high wheels capable of crossing rutted roads, muddy flats, and the nonroads of the prairie, and a floor that was curved upward at both ends to prevent cargo from shifting on steep grades.