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]: If an atom of hydrogen gives up one electron, what is its overall charge?  
 (A) -1 (B) +1 (C) -2 (D) +2
[EX A]: B

[EX Q]: 22 Sandy is conducting an investigation to find out which food his dog likes best. Which is the manipulated variable in his investigation?  
 (A) The color of his dog's food dish (B) The kind of food he gives his dog (C) The amount of food he gives his dog (D) The time of day he feeds his dog
[EX A]: B

[EX Q]: Which of these factors causes water to evaporate the fastest?  
 (A) high temperatures (B) high humidity (C) slow winds (D) slow runoff
[EX A]:
A