In a cathode-ray tube, an electron moves with uniform acceleration in a straight line, increasing its speed from $4 \times 10^{3}\,\text{m s}^{-1}$ to $2 \times 10^{7}\,\text{m s}^{-1}$ across a distance of $10\,\text{mm}$. What is the electron's acceleration?
- A$2 \times 10^{3}\,\text{m s}^{-2}$
- B$2 \times 10^{6}\,\text{m s}^{-2}$
- C$2 \times 10^{13}\,\text{m s}^{-2}$
- D$2 \times 10^{16}\,\text{m s}^{-2}$