Here's a problem to solve: In science class, a student obtains 20 mL of an acid solution. A small amount of acid is added to a substance to detect the presence of copper. What should be done with the excess acid solution?

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

- A: Pour the acid into a trash can.
 
- B: Neutralize the acid before pouring it down a sink.
 
- C: Return the acid to the teacher's stock bottle.
 
- D: Allow the water to evaporate from the acid solution.
 