There Are Approximately 40,000 Species of Trees in Tropical Rainforests

There are approximately 40,000 species of trees in tropical rainforests.There are only 50 species of trees north of the Alps in Europe.The greater species diversity in tropical rainforests might be explained by any combination of these factors except

A) higher productivity.
B) a more rapid rate of speciation.
C) a longer species diversification time.
D) greater likelihood of species extinction due to climate.
E) a larger geographic area, enabling greater reproductive isolation.