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.
Example: Which part of a bicycle BEST moves in a circle? 
 (A) Seat (B) Frame (C) Foot pedal (D) Kickstand
Example solution: C
Example explanation: Seat, frame and Kickstand are static parts of the bicycle, even when bicycle moves. Foot pedal moves in a circle as bicycle moves.

Problem: How can plants most likely improve air quality?  
 (A) by absorbing nutrients (B) by producing oxygen (C) by producing sugar (D) by absorbing water

Solution: B