You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

[EX Q]: Water in the solid phase has a crystal structure which keeps molecules farther apart than water at certain temperatures in the liquid phase. This relationship explains which property?
(A) the presence of more impurities in ice than in liquid water (B) the ability of ice to float on liquid water (C) the release of heat when liquid water turns into ice (D) the cooling of liquid water as it flows over ice
[EX A]: B

[EX Q]: How many valence electrons does selenium have?
(A) 3 (B) 5 (C) 6 (D) 8
[EX A]: C

[EX Q]: Which of the following materials are direct products of photosynthesis?
(A) fats and starches (B) oxygen and sugar (C) proteins and amino acids (D) carbon dioxide and water
[EX A]:
B