The correct option is D All of the above.
Transpiration is considered as a necessary evil in plants by Curtis. The loss of water from the aerial parts of the plant creates a tension that causes the water column to be pulled up from the soil. This is called transpiration pull.
Hence transpiration is the major force responsible for the ascent of sap. Due to transpiration, there is an uninterrupted water supply to the plant. The continuous water supply is essential for photosynthesis and also provides the plant with necessary minerals.
As trees release water into the atmosphere by transpiration, the surrounding air also gets cooled.