Here's a problem to solve: Some paper mills use machines that make paper without any wood called "wood-free" paper. These machines make paper from materials such as cotton and rice waste. Which problem does using wood-free paper affect most?

Among the 4 following options, which is the correct answer?

- A: increased use of fossil fuels
 
- B: decrease in water supply
 
- C: loss of animal habitats
 
- D: pollution of air
 