You are interested in determining which of two brands of light bulbs, brand A and brand B, lasts longer under differing conditions of use. Fifty Bovano lamps are fitted with brand A light bulbs and 50 Bulbrite lamps are fitted with brand B light bulbs. Each light bulb is left on for 20,000 hours straight. Light bulb life is then measured for each bulb, and the average light bulb life for the two brands is compared. What is wrong with this experimental design?

Nothing is wrong with this design.
The type of lamp is a confounding variable.
Not enough light bulbs of each type are used in the study.
The experiment should have been conducted on more than two brands of lamps.