题目选项分析

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.

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 floors curving upward at their ends so that it prevented cargo from shifting on steep grades.