Consider the two statements:

I. Elevated atmospheric CO₂ increases the instantaneous rate of photosynthesis in C₃ plants.
II. Current availability of atmospheric CO₂ level is limiting to the C₃ plants.

1. Both I and II are correct and II explains I
2. Both I and II are correct but II does not explain I
3. I is correct but II is incorrect
4. Both I and II are incorrect