Consider the following two statements:
I. The evolution of ${\mathrm{C}}_4$  photosynthesis is probably one of the strategies for maximizing the availability of ${\mathrm{CO}}_2$ while minimizing water loss.
II. Plants with ${\mathrm{C}}_4$ photosynthesis close their stomata during day and open them in night.
1. Both I and II are correct
2. I is correct and II is incorrect
3. I is incorrect and II is correct
4. Both I and II are incorrect

Which one of the following elements in plants is not remobilised?