Which sentence from the passage supports the idea that the "world is chiefly indebted" to james watt and george stephenson for developing the steam engine?

If these were the missing choices: 

A. The first train consisted of thirty-four cars weighing, all told, ninety tons.
B. Before the time of Watt, the steam engine was exclusively a steam pump—slow and wasteful of fuel.
C. The idea of using steam for driving stationary machinery originated in the early centuries.
D. Watt made it a quick, powerful, and efficient engine, requiring only a fourth as much fuel as before.

My answer is D. WATT MADE IT A QUICK, POWERFUL, AND EFFICIENT ENGINE, REQUIRING ONLY A FOURTH AS MUCH FUEL AS BEFORE.

Though the passage is not given, I chose option D because it gives the benefit that others experienced from Watt's contribution.