题目选项分析

A pair of architects in Britain, who say that giant arches, bridges, and walls made of artificial bone could be easier to design and build than conventional structures, and already designed a number of structures, including a bridge, for showing how their idea would work.

A pair of architects in Britain, who say that giant arches, bridges, and walls made of artificial bone could be easier to design and build than conventional structures, have already designed a number of structures, including a bridge, to show how their idea would work.