Out of the following given choices;
A) limited sunlight
B) shortage of water
C) excess carbon dioxide
D) freezing temperatures
The answer is C. Excess carbon dioxide would not be a limiting factor but rather an expediting factor. Photosynthesis involves the photolysis of water and the reduction of carbon dioxide to carbohydrates. The photolysis of water is enabled by energy from sunlight.
Freezing temperatures would limit photosynthesis since the enzymes involved in the process would be working at below optimal temperatures hence would be slow in reactions.