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

Paul Ehrlich suggested the Rivet Popper Hypothesis,in which he compared an ecosystem and species to . . . . . . and . . . . . . respectively.

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

Match the following with respect to different categories of the red list. Choose the correct option.

Column-$I$	Column-$II$
$i$. Extinct	$a$. Species whose members survive only in captivity.
$ii$. Extinct in wild	$b$. Rapid population decline of $50\%$ to more than $70\%$ over the previous $10$ years.
$iii$. Endangered	$c$. Species in which the last individual has died.
$iv$. Vulnerable	$d$. Rapid population decline of $30\%$ to more than $50\%$ over the previous $10$ years.

Initially $A$ biodiversity hot spots were identified but subsequently nine more have been added to the list,bringing the total number of biodiversity hot spots in the world to $B$. These hot spots are the regions of accelerated habitat loss. Three of these hot spots—Western Ghats and Sri Lanka,Indo-Burma,and Himalaya—cover our country's exceptionally high biodiversity regions. Although all the biodiversity hot spots put together cover less than $C$ $\%$ of the earth's land area,the number of species they collectively harbour is extremely high,and the strict protection of these hot spots could reduce the ongoing mass extinctions by almost $D$ $\%$. $A, B, C$ and $D$ in the paragraph refer to:

The total number of biodiversity hotspots currently identified worldwide is $.........$.