Why do prices generally go up over time?

Answer: Money supply increases

Money supply increases ✓ — Correct! When the money supply grows faster than the amount of goods and services, each dollar buys less, pushing the general price level up. This is a leading explanation for sustained inflation, though economists still debate how large this effect is compared to other forces.

Demand always rises — Wrong. Demand goes up and down for different products and doesn't always rise. While strong demand can pull prices up for a while, it isn't a constant force behind the general upward trend.

Products get better quality — Wrong. Better quality can raise the price of specific items, but it doesn't explain why prices in general rise over time, including for goods whose quality hasn't changed.