When a Land Bridge Was Reestablished Between North and South

When a land bridge was reestablished between North and South America at the end of the Pliocene,what happened?

A) Nothing happened because the major mammal groups had not evolved differently since the previous connection had been broken
B) Only the porcupine,armadillo,and opossum invaded from the south and survived
C) Both continents immediately dropped in diversity
D) Many hoofed animals moved north and displaced North American fauna
E) There was an enormous exchange of species in both directions