Choose the correct labelling for the given figure.

$A-$ The $C_3$ and $C_4$ plants respond differently to $CO_2$ concentrations.
$R -$ The concentration of $CO_2$ in the atmosphere is between $0.03$ and $0.04$ percent. An increase in concentration up to $0.05$ percent can cause an increase in $CO_2$ fixation rates.

If a chemical process is affected by more than one factor,then its rate will be determined by:

$A$ plants have a higher temperature optimum than the plants adapted to $B$ climate. Here $A$ and $B$ refer to:

The figure shows the effect of light on the rate of photosynthesis. Based on the graph,answer the following questions:
$(a)$ In which region/s (indicated by arrows) is light a limiting factor?
$(b)$ What could be the limiting factor/s in the region where the rate of photosynthesis becomes constant?
$(c)$ What does the point where the curve flattens represent?

The value of $Q_{10}$ for photosynthesis is