In the Amylase Activity Experiment, the Development of a Blue-Black

In the amylase activity experiment, the development of a blue-black color upon the addition of iodine-potassium-iodide to the test tube indicates that

A) the starch has been broken down.
B) the starch has been denatured.
C) amylase is functioning at its optimum temperature.
D) the starch has not been broken down.
E) glucose is present in the test tube.