In the $Rivet$ $Popper$ hypothesis,what do the rivets represent?

The largely tropical ............. rain forest in South America has the greatest biodiversity on earth.

In global biodiversity of plants,which of the following statements is correct?

Which part of the world has a high density of organisms?

Tropical regions show the greatest level of species richness because:
$A$. Tropical latitudes have remained relatively undisturbed for millions of years,hence more time was available for species diversification.
$B$. Tropical environments are more seasonal.
$C$. More solar energy is available in the tropics.
$D$. Constant environments promote niche specialization.
$E$. Tropical environments are constant and predictable.
Choose the correct answer from the options given below.

How many biodiversity hotspots are there in the world?