TASK DEFINITION: In this task, you need to answer basic science questions. For each question, several terms are intentionally masked with ***. This masking can cover very few or many of the question words. Clearly, if masked terms are important, the modified question will be impossible to answer. Please indicate the correct answer with one of the following responses: "A", "B", "C", "D" or "E". While "A"-"D" correspond to the answer options provided in the input, "E" represents "I don't know" for questions that do not provide enough information. Respond via "E" if the question is not answerable. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D', 'E'.
PROBLEM: Question: *** *** is an *** of a  (A) liquid changing to a solid (B) solid changing to a liquid (C) gas changing to a solid (D) gas changing to a liquid.

SOLUTION: E.

PROBLEM: Question: The *** of the *** allowed which of the following to take place?  (A) the discovery of cells (B) the identification of weather patterns (C) detailed observation of planets (D) communication between distant citie.

SOLUTION: E.

PROBLEM: Question: A company plants trees on a bare hillside. Which of these is the BEST reason for *** the trees?  (A) The trees provide oxygen for the soil. (B) The trees prevent soil from washing away. (C) The trees make shade for animals living there. (D) The trees cause animals to move to other places.

SOLUTION:
B.