In the diagram, two full pulses are displayed on the screen of a cathode-ray oscilloscope. The screen is overlaid with a grid made of $1\,\text{cm}$ squares. The time-base setting is $1\,\mu\text{s cm}^{-1}$. What is the duration of each pulse?
- A$2\,\mu\text{s}$
- B$3\,\mu\text{s}$
- C$4\,\mu\text{s}$
- D$6\,\mu\text{s}$