Which aspect of mass production allows a broken machine to be fixed quickly using an identical item?

A. specialization

B. assembly line

C. division of labor

D. interchangeable parts

The picture below shows president richard nixon and the first lady standing before the great wall of china in 1972. they are smiling - as are the chinese with them. when this picture was shown on american television, americans were aware that it was a historic moment. what are two reasons why this moment was important for both china and the united states?