In $Pheretima$,fertilization occurs in $.........$.

$A$ - Earthworms are farmer's friends.
$R$ - They help in the breakdown of complex organic matter as well as in loosening of the soil.

In earthworm,which of the following statements is correct regarding its development?

Following are the statements about the prostomium of an earthworm.
$(a)$ It serves as a covering for the mouth.
$(b)$ It helps to open cracks in the soil into which it can crawl.
$(c)$ It is one of the sensory structures.
$(d)$ It is the first body segment.
Choose the correct answer from the options given below.

The calciferous glands present in the stomach of an earthworm secrete:

What is the function of the typhlosole in an earthworm?