The Fossil Record Indicates That at One Time Marsupials Were

The fossil record indicates that at one time marsupials were common to both Australia and South America,but today most South American marsupials have become extinct.The most probable explanation for marsupials being common to Australia yet not very common to South America today is that

A) South American marsupials were displaced by placental mammals when a land bridge formed between North America and South America about seven million years ago.
B) marsupials were able to flourish in South America because of its isolation from other land masses.
C) placental mammals are less fully developed than marsupials when born and therefore have a better chance of survival after birth.
D) South American and Australian marsupials interbreD.
E) marsupials can survive only in warm climates like Australia.