A student used a potometer to determine the rate of water loss from a plant through transpiration. The internal diameter of the capillary tube and the distance travelled by the bubble in $30\ \text{s}$ were noted. The volume of water moved $= \pi r^2 \times$ distance moved by the bubble. Which calculation correctly shows how to work out the rate of transpiration in $\text{mm}^3\ \text{s}^{-1}$?
- A$\frac{\pi(1.8^2 \times 40.0)}{30}$
- B$\pi(1.8^2 \times 40.0) \times 30$
- C$\frac{30}{\pi(0.9^2 \times 40.0)}$
- D$\frac{\pi(0.9^2 \times 40.0)}{30}$