In the circuit $PQR$ shown, three batteries and three identical resistors are connected together. The batteries have negligible internal resistance. What is the potential difference between points $P$ and $Q$?
- A$1.5\,\text{V}$
- B$2.1\,\text{V}$
- C$7.1\,\text{V}$
- D$12.1\,\text{V}$