With reference to factors affecting the rate of photosynthesis, which of the following statements is not correct?

1. A
   Increasing atmospheric ${\text{CO}}_2$ concentration upto $0.05\%$ can enhance ${\text{CO}}_2$ fixation rate
2. B
   ${\text{C}}_3$ plants respond to higher temperatures with enhanced photosynthesis while ${\text{C}}_4$ plants have much lower temperature optimum
3. C
   Tomato is a greenhouse crop which can be grown in ${\text{CO}}_2$ - enriched atmosphere for higher yield
4. D
   Light saturation for ${\text{CO}}_2$ fixation occurs at $10\%$ of full sunlight