You are given a science question (easy-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.

Which of these warms most of the air, water, and land on Earth?  
 (A) Coal (B) Electricity (C) Sunlight (D) Wind
C

Which involves the greatest variety of cell types?  
 (A) a tissue (B) an organ (C) an organ system (D) an organism
D

What property of water best helps aquatic life survive in lakes during the winter?  
 (A) water has a high specific heat capacity (B) water has a high surface tension (C) water is less dense as a solid than as a liquid (D) water is a polar molecule

C