Question 2
Why is water put in bag C?
The right answer is the one marked above.
So that leaf C is in a sealed bag with a liquid, exactly like leaf D. The water absorbs no carbon dioxide worth speaking of. It is there to make the two bags identical in everything but the gas.
Leaf C already gets all the water it needs through the xylem, from the roots. Water in a bag round a leaf is not a water supply — it is a control.