OG 2016 verbal 33题

小习

Developed by Pennsylvania's Palatine Germans about 1750, Conestoga wagons, which had high wheels capable of crossing rutted roads, muddy flats, and the nonroads of the prairie, and floors curve upward on their ends so that they prevent cargo from shifting on steep grades.
这句话错在哪了？？？

sangjinghui9

上面那句话没有谓语吧？