A

In a parallel combination: Each bulb receives the full supply voltage. This means that the bulb with the highest power rating (which corresponds to the highest wattage given a constant voltage) will glow the brightest. Therefore, the bulb glows most brightly in parallel.

In a series combination: The total voltage is divided among the bulbs. The total current through the circuit is the same for all bulbs, and the brightness depends on the power rating of each bulb. The bulb with the lowest power rating (because it has the highest resistance) will glow the brightest due to receiving a larger share of the voltage drop compared to the others. Therefore, the bulb glows most dully in series.