Which one of the listed short-run cost curves is the only one that is never 'U' shaped?

1. AVC, ATC and MC all fall, reach a minimum, then rise, giving the U shape. 2. AFC = TFC / Q falls continuously toward the X-axis without ever rising. 3. A curve that only falls cannot be U shaped, so the AFC curve is never U shaped. 4. ATC (A), AVC (B) and MC (D) are all U shaped. Hence the average fixed cost curve. _Source: ICAI BoS CA Foundation Paper 4 Business Economics, Ch 3 Unit II "Theory of Cost", p.6_