The number of cars produced has decreased. The need for custom manufacturing has increased. The efficiency of manufacturing plants has increased. The number of countries producing cars has decreased.
I gave my students this multiple choice question: Which of the following statements best describes how the use of interchangeable parts has affected car manufacturing?

Only one answer is correct among these 4 choices:
- The number of cars produced has decreased.
- The need for custom manufacturing has increased.
- The efficiency of manufacturing plants has increased.
- The number of countries producing cars has decreased.

Could you tell me which one is correct?

The efficiency of manufacturing plants has increased.