Answer:
D. Cup 4 had the lowest rate of photosynthesis because it had the least CO2.
Step-by-step explanation:
Carbondioxide gas is the main reactant for the process of photosynthesis which decides the production of food in the leaves. If plants has high amount of carbondioxide gas and water so in the presence of sunlight it produces more food in the leaves in the form of glucose so we can conclude that the lowest rate of photosynthesis occurs due to presence of least concentration of carbondioxide gas in the cup 4.