The development of a system of mass production in manufacturing meant that

The development of a system of mass production in manufacturing meant that productivity increased while cost of production went down.

A good example is Henry Ford's Model T  car. Henry Ford designed a method of building a car by passing the car through an assembly line such that a mere chassis  at the start of the line ended up a complete vehicle driven under its own power as it reached the end of the line.  By using the assembly line, Henry Ford was able to combine accuracy , continuity and speed such that a complete Model T car was leaving the assembly line every 10 seconds.

In so doing, Ford was able to mass produce cars, meet customer demand and cut production cost and, ultimately ,the sale price of the car from 800 dollars to just 260 dollars, a very affordable price at the time.

the answer is b: an economic crisis throughout the country.