instruction:
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.
question:
What is the primary function of white blood cells in humans?  
 (A) carry oxygen (B) fight disease (C) grow tissues (D) remove waste
answer:
B


question:
Which property of air does a barometer measure?  
 (A) speed (B) pressure (C) humidity (D) temperature
answer:
B


question:
Rolanda is growing tomato plants in her garden. She has created a compost pile and has been adding compost around her tomato plants to help fertilize them. Compost is solid waste in which organic material is broken down by microorganisms in the presence of oxygen to where it can be safely stored, handled, and applied to the environment. On what does Rolanda primarily rely in order for composting to work?  
 (A) producers (B) consumers (C) scavengers (D) decomposers
answer:

D