The diagram shows a simple electrical circuit with a main switch and three parallel branches, each containing a lamp and a switch (S1, S2, S3). Explain how to operate the circuit to achieve the follow

b)

i) To switch on only one lamp, the student must close the main switch and one of the parallel branch switches. For example, to light the lamp connected to S2, the student closes switches $\text{S}_1$ and $\text{S}_2$.
The student closes switches $\boxed{\text{S}_1 \text{ and } \text{S}_2}$ (or $\text{S}_1 \text{ and } \text{S}_3$).

ii) To switch on two lamps, the student must close the main switch and both parallel branch switches.
The student closes switches $\boxed{\text{S}_1, \text{S}_2 \text{ and } \text{S}_3}$.