explain the difference between a gyrus, a sulcus and a fissure.
a) Gyri = Grooves; Sulci = Folds; Fissures = Ridges

b) Gyri = Ridges; Sulci = Grooves; Fissures = Valleys

c) Gyri = Folds; Sulci = Grooves; Fissures = Ridges

d) Gyri = Folds; Sulci = Ridges; Fissures = Grooves