What is the total number of biodiversity hotspots in the world?

In India, we find mangoes with different flavours, colours, fibre content, sugar content and even shelf-life. The large variation is on account of

Which of the following is true for species diversity?

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.

The number and types of organisms present on Earth refer to:

The Amazon rain forest is estimated to produce what percentage of the total oxygen in the Earth's atmosphere through photosynthesis (in $\%$)?