Answer:
The sentence that best states the main idea of the passage is:
D. The changes Henry Ford introduced in the assembly line allowed a greater number of goods to be produced in a shorter amount of time.
This sentence captures the main focus of the passage, which is the impact of Henry Ford's changes to the assembly line on the production of goods. The passage discusses how Ford's innovations revolutionized manufacturing by increasing efficiency and productivity through the use of assembly line techniques. It highlights the significance of these changes in American industry during the 1910s.