It has been necessary to refer repeatedly to the effects of the two world wars in promoting all kinds of innovation.It should be【C1】______also that technological innovations have【C2】______the character of war itself by the【C3】______of new mechanical and chemical devices.One weapon developed【C4】______World War II deserves a special mention.The【C5】______of rocket propulsion （推进力）was wellknown earlier，and its possibilities as a 【C6】______of achieving speeds sufficient to escape from the Earth’s gravitational （引力的）pull had been【C7】______out by the Russian and the American scientists.The【C8】______built an experimental liquid-fuelled rocket in 1926.【C9】______，a group of German and Romanian pioneers was working across the same lines，and in the 1930s，it was this team that developed a rocket【C10】______of delivering a warhead hundreds of miles away.Reaching a height of over 100miles，the V-2rocket【C11】______the beginning of the Space Age，and members of its design team were【C12】______in both the Soviet and United States space programs after the war.Technology had a tremendous social【C13】______in the period 1900—1945.The automobile and electric power，on the other hand，radically changed both the scale and the quality of 20th-century life，【C14】______a process of rapid urbanization and a virtual revolution【C15】______living through mass production of household goods and【C16】______.The rapid development of the airplane，the cinema，【C17】______radio made the world seem suddenly smaller and more【C18】______.The development of many products of the chemical industry further transformed the life of【C19】______people.In the years following 1945the constructive and creative opportunities of modern technology could be exploited，【C20】______the process has not been without its problems.

【C1】（）

A．observed
B．notified
C．commented
D．detected