If the rates of transpiration and water absorption of a flowering plant are measured over a period of $24$ hours,it is found that the rate of transpiration reaches its peak at about mid-day and then declines,whereas the peak for water absorption is reached approximately two hours later. Which one of the following statements provides the best explanation of these results?

• A
  There is a temporary reduction of light intensity at mid-day,which reduces the rate of transpiration.
• B
  Water absorption is mainly due to root respiration and this is affected by soil temperature,which does not reach a maximum for some hours after the maximum air temperature has been reached.
• C
  The high rate of transpiration causes a water deficit which results in stomatal closure and an increased concentration of leaf cell sap,which in turn causes continued water uptake.
• D
  The high light intensity results in high internal oxygen concentrations and so increases water uptake.