What is component 4 in figure T-1?

Explanation
Component 4 is the battery in Figure T-1. The resistor and transistor are components 1 and 2, and the ground symbol is component 5, so the other choices point to different parts.

Component 4 is the battery in Figure T-1. The resistor and transistor are components 1 and 2, and the ground symbol is component 5, so the other choices point to different parts.