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]: Which of these describes water in a solid state?  
 (A) Vapor rising in the sky (B) Hail during a storm (C) Waves crashing on the seashore (D) Rain falling from the clouds
[EX A]: B

[EX Q]: Scientists have measured the rate of growth of the Atlantic Ocean basin to be about 2 to 3 cm per year. This type of activity coincides with the formation of ridges on the ocean floor. What is the most likely cause of this activity?  
 (A) erosion from tidal action (B) the deposition of sediment (C) the flow of continental basalt (D) movement from tectonic plates
[EX A]: D

[EX Q]: What most likely happens when a cold air mass comes into contact with a warm, moist air mass?  
 (A) The sky becomes clear. (B) Rain or snow begins to fall. (C) Cold air is pushed to high altitudes. (D) Warm air is pushed to ground level.
[EX A]:
B