A. (althougth flowers do need sun) is not correct, as all the flowers were in the sun, so it doesn't explain the results.
B. is also wrong as the "vinegar flowers" are dead.
C. Plants to need water to survive, but more evidence is needed to know for sure (such as a vase without water- maybe they don't need water, but die in soda or vinegar?)
D. This is true- we clearly see that the plants in water well a lot better off than those in soda or vinegar!