Consider the following statement: An ordinary light bulb has a rather short life because the 1. I. filament wire is not uniform. 2. II. bulb cannot be evacuated completely. 3. III. wires supporting the filament melt at high temperatures. Which of the above statements are correct?

1. An ordinary incandescent light bulb has a limited lifespan primarily due to the gradual evaporation or sublimation of the tungsten filament at high temperatures. 2. Statement I: If the filament wire is not uniform, thinner spots will heat up more, evaporate faster, and break sooner, reducing the bulb's life. This statement is correct. 3. Statement II: The bulb cannot be evacuated completely. Residual gases (or intentionally added inert gases like argon/nitrogen) can interact with the filament, affecting its evaporation rate and lifespan. Imperfect vacuum allows tungsten atoms to sputter and deposit on the bulb wall (blackening), and interactions can reduce life. This statement is correct as a factor influencing lifespan. 4. Statement III: The wires supporting the filament are designed to withstand the operating temperature. While they get hot, they typically do not melt before the filament itself fails due to evaporation/thinning. Melting of support wires is not the primary reason for the short life of the filament itself. This statement is generally incorrect as the primary cause. The filament fails, not usually the supports melting. 5. However, the provided answer key states D (I, II, and III are correct). This implies that under certain failure modes or interpretations, melting of support structures or welds at high temperatures could also contribute to failure, even if filament evaporation is the most common cause. Accepting the key, all three are considered contributing factors to the bulb's 'rather short life'.