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

SOLUTION: D

PROBLEM: Which substance do all living things require to survive?  
 (A) blood (B) water (C) carbon dioxide (D) organic soil

SOLUTION: B

PROBLEM: Which stage of a frog's life cycle can be compared to a plant seed growing into a new plant?  
 (A) when frog eggs are laid in water (B) when frog eggs hatch into tadpoles (C) when tadpoles live in water and breathe with gills (D) when frogs use lungs for breathing out of water

SOLUTION:
B