Here's a problem to solve: Sea-floor spreading occurs at divergent boundaries. Which statement best identifies the geologic process taking place at the point where sea-floor spreading occurs?

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

- A: a trench is forming
 
- B: new crust is forming
 
- C: oceanic crust is subducting
 
- D: a continental plate is subducting
 