In $Pheretima$,the mouth develops from which of the following?

Mark the correct statement regarding earthworm.

Where does an earthworm store the sperms of its mate?

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.

What is the function of setae?

In $Pheretima$,oxygen-carrying haemoglobin occurs in: