Four identical rods each have a square cross-section. They are arranged side by side, and their total width is measured using vernier calipers, as shown. The reading is $(8.4 \pm 0.1)\,\text{mm}$ and the zero reading on the calipers is $(0.0 \pm 0.1)\,\text{mm}$. What is the width of a single rod?
- A$(2.10 \pm 0.025)\,\text{mm}$
- B$(2.10 \pm 0.05)\,\text{mm}$
- C$(2.1 \pm 0.1)\,\text{mm}$
- D$(2.1 \pm 0.2)\,\text{mm}$