In this subtask, you will answer a simple science question. Please indicate the correct answer. If you're not sure about the answer, choose the last option "I don't know". Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D', 'E'. The "A"-"D" responses correspond to the answer options mentioned in the input. There is a 5th option "E" which should be used for questions for which you're not sure about the answer (e.g., when the questions do not provide enough information to answer).

[EX Q]: Question: What tool is used to determine the mass of an object?  (A) Balance (B) Meter stick (C) Thermometer (D) Graduated cylinde?
[EX A]: A.

[EX Q]: Question: The tailgate of a pickup truck was rusting where the paint was scratched off. What chemical change had occurred?  (A) Liquidation (B) Conservation (C) Oxidation (D) Reductio?
[EX A]: C.

[EX Q]: Question: On a warm sunny afternoon, ocean water splashed onto a rock. A short time later, the rock was dry. Which statement best explains what happened to the water on the rock?  (A) Heat caused the water to become a gas. (B) Heat melted the water and it disappeared. (C) Salt caused the water to become a gas. (D) Salt melted the water and it disappeared?
[EX A]:
A.