B. Whether the starch in glutinous rice is hydrolyzed can be completely tested by iodine water. If the solution turns blue, the starch is not completely hydrolyzed, otherwise it is completely hydrolyzed, so B is correct;

C. Starch in glutinous rice can be hydrolyzed to glucose under the catalysis of dilute sulfuric acid or enzymes in human body, so C is wrong;

D. Diabetic patients can't eat zongzi, because glutinous rice contains a lot of starch that can be hydrolyzed to produce glucose, which will increase blood sugar, so D is wrong;

So choose B.