The experimental method includes the following steps: dark treatment → partial illumination → illumination → alcohol decoloration → iodine rinsing → color observation → phenomenon analysis, and a conclusion is drawn.

There are two groups of control experiments in this experiment: the experimental variable of one group is the presence or absence of chloroplast leaves. After dropping iodine solution, the silver edge part does not turn blue, indicating that there is no starch in this part, and the green leaf part turns blue, indicating that starch is produced here, and it can be concluded that photosynthesis occurs in the green part of the leaf; The experimental variable of the other group is whether there is light or not, and the uncovered part of the leaf turns blue, which means that starch is produced here, but the covered part of the leaf does not turn blue, which means that starch is not produced in this part. It can be concluded that light is a necessary condition for plant photosynthesis, and starch can be synthesized through photosynthesis. Photosynthesis needs to consume carbon dioxide, which is not in line with the problem.

So choose d