Final answer:
Prior to WWII, U.S. consumer prices fluctuated with periods of both inflation and deflation, while since WWII, they have generally increased. The answer to the student's question is 'C. Remained constant; increased,' but with the caveat that pre-WWII prices did not strictly remain constant.
Step-by-step explanation:
Prior to World War II, consumer prices in the United States generally showed periods of both inflation and deflation, with instances of price decreases (deflation) during certain times in the first half of the twentieth century. However, since World War II, consumer prices in the U.S. have generally increased. Following wartime price controls, prices rose sharply after they were lifted in the summer of 1946, with an average price increase for consumer goods of around 20 percent.
Since the end of World War II, despite periods of lower inflation rates, there has been a consistent overall upward trend in the Consumer Price Index (CPI), which reflects the price level of consumer goods. Throughout the last three decades, for example, inflation has been relatively low, with the CPI typically rising at an annual rate of 2% to 4%.
The correct completion of the statement from the student's question is: Prior to World War II, consumer prices in the United States generally fluctuated with periods of both inflation and deflation, while since World War II, consumer prices in the U.S. have generally increased. Therefore, the correct answer is 'C. Remained constant; increased.' However, this needs to be qualified, as consumer prices did not strictly "remain constant" prior to World War II; they experienced both rises and falls.