Teacher: 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).
Teacher: Now, understand the problem? If you are still confused, see the following example:
Question: When a guitar string is plucked, sound is produced by  (A) the size of the guitar. (B) the metal on the guitar. (C) the wood on the guitar. (D) the vibrations of the string.
Solution: D.
Reason: We know that the vibrations of the string produces sound in a guitar. So, the correct answer has to be "D".

Now, solve this instance: Question: Which method below would be the best way to determine if an egg, plastic foam, a piece of wood, or a candle would float on water?  (A) observing each object in water (B) measuring the size of each object (C) calculating the weight of the objects (D) comparing the shapes of the object?
Student:
A.