Verbal Reasoning — Classification (Always/essential component): A “bulb” must necessarily have which of the following? Assume the conventional electric bulb context used in reasoning questions; separate core parts from conditions of use. Choose the component that a bulb always has.

Concept/ApproachIn classic reasoning items, “bulb” means an incandescent electric bulb whose essential working part is the filament. Current and light are conditions when powered; glass envelopes can vary in material/form but the filament is the key internal element.

Final AnswerFilament.

Note: Modern LED bulbs differ internally, but traditional exam logic assumes incandescent construction.