Which statement(s) is/are true?
a. slow spreading centers tend to have developed rift valleys; fast spreading centers often lack rift valleys.
b. slow spreading centers are often characterized by a central swell; fast spreading centers have no such swell.
c. fast spreading centers have prominent ridges and rugged topography; slow spreading centers have rather smooth topographies.
d. slow spreading centers have prominent ridges and rugged topography; fast spreading centers have rather smooth topographies.
e. fast spreading centers tend to have developed rift valleys; slow spreading centers often lack rift valleys.