Why In Figure T-1, component 3 is drawn as a circle with an X (crossed lines) inside it, which is the standard schematic symbol for an incandescent lamp or indicator bulb. The circle represents the glass envelope and the crossed lines stand for the filament supports. Figure T-1 also contains a resistor (zigzag or rectangle), a transistor (circle with three leads and an arrow), and a battery, so learning which number goes with which symbol is what this question tests.
Watch out The transistor is the nearby symbol with three leads and an arrowhead on the emitter, and a ground symbol is a set of stacked horizontal bars or a triangle at the end of a single lead, not an enclosed circle.
Circle with an X = lamp lit up. In T-1: 1 resistor, 2 transistor, 3 lamp, 4 battery.