The circuit diagram contains a battery, three lamps X, Y and Z, and three switches $S_1$, $S_2$ and $S_3$. Lamp X is not lit, while lamps Y and Z are illuminated. Which switches are closed?
- A$S_1$ and $S_2$ only
- B$S_1$ and $S_3$ only
- C$S_2$ and $S_3$ only
- D$S_1$, $S_2$ and $S_3$