The correct option is D Both B and C.
In plants, transpiration is the loss of water from leaves and stems. It is affected by humidity and temperature. Potometer is a tool used for measuring the rate of transpiration. The rate of transpiration cannot be accurately determined using a potometer because all the water that is taken by the plant is not involved in transpiration. Also, potometer only measures the rate of uptake of water. Transfer of water at the leaves can be measured using other scientific instruments. Thus the correct answer is option D.