The diagram represents a circuit with a d.c. power supply, a motor and a variable resistor. Three ammeters X, Y and Z indicate the current in different sections of the circuit. Ammeter X reads $4.0\,\text{A}$. Which statement is correct?
- AThe readings on Y and Z are both less than $4.0\,\text{A}$.
- BThe readings on Y and Z are both equal to $4.0\,\text{A}$.
- CThe readings on Y and Z are both greater than $4.0\,\text{A}$.
- DThe reading on Z is zero.