a) On a cloudy day, the rate of photosynthesis decreases since the intensity of sunlight decreases.
b) No rainfall in the area decreases the rate f photosynthesis since the amount of water decreases which is an important substrate for photosynthesis.
c) Good manure in the area will increase the rate of photosynthesis since the nutrients supply is good.
d) When the stomata is blocked the rate of photosynthesis decreases since the exchange of gases cannot take place easily.