Here's a problem to solve: Why is water from an aquifer more likely to be cleaner than water from other sources?

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

- A: because it forms where fresh and salt water meet
 
- B: because it receives water directly from precipitation
 
- C: because it rises to the surface near the ocean
 
- D: because pollutants are filtered by rock and soil deep within Earth
 