Excretory organs of Earthworm are

Earthworms are known for having which of the following?

The female genital aperture in earthworm is present ventrally on the segment: (in $^{th}$)

Match the regions of the earthworm based on the clitellum:
$P$ - Segments $14$ to $16$
$Q$ - Segment $17$ to the last segment
$R$ - Segments $1$ to $13$
Identify the correct sequence for the Pre-clitellar region,Post-clitellar region,and Clitellar region,respectively.

The presence of earthworms in the soil is indicated by:

Earthworms increase the . . . . . . of the soil.