Modern-day snakes are believed to evolve from four-legged lizards, but scientists were divided over whether that phase of evolution occurred on land or in the sea; the recent discovery of fossils of a land-dwelling snake with two legs provides new information for the ongoing debate.

A. evolve from four-legged lizards, but scientists were

B. have evolved from four-legged lizards, but scientists are

C. evolve from four-legged lizards, but scientists are

D. have evolved from four-legged lizards, but scientists were

E. be evolving from four-legged lizards, but scientists were


please explain between B and D