Which segment contains the mouth in an earthworm?

The earthworm does not have a skeleton,but during burrowing,its posterior end becomes turgid and acts as a hydraulic skeleton. This is due to:

Pharyngeal nephridia of Earthworm $Pheretima$ occur in segments

How many pairs of pores of spermathecae are present in an earthworm (in $pairs$)?

Identify the incorrect statements among the following:
$(a)$ In earthworm,a single male genital pore is present.
$(b)$ Setae help in locomotion of earthworm.
$(c)$ The muscular layer in the body wall of earthworm is made up of only circular muscles.
$(d)$ Typhlosole is a part of the intestine of earthworm.

$Pheretima$ $posthuma$ is very useful as: