What reason is given for the stability of the arch? A.A concrete foundation supports the arch. B.The arch is built with wedge-shaped blocks. C.The Romans made a strong type of concretE. D.The pressure flows up to the keystonE.
A.A B. B.The C. C.The D. D.The E.
【参考答案】
B 解析：The professor says The round arch is extremely stro......