The diagram presents two full pulses on the screen of a cathode-ray oscilloscope. A grid made up of $1\,\text{cm}$ squares is drawn across the screen. The time-base setting is $1\,\mu\text{s cm}^{-1}$. How long does each pulse last?
- A$2\,\mu\text{s}$
- B$3\,\mu\text{s}$
- C$4\,\mu\text{s}$
- D$6\,\mu\text{s}$