Select the correct statement from the following.
(A) In most of the invertebrates, excretory structures are in complex tubular forms.
(B) Vertebrates have simple tubular organ as excretory structure like kidney. 
(C) Protonephridia is primarily concerned with excretion.
(D) Protonephridia are excretory structure in rotifers, some annelids and cephalochordates (Amphioxus).  

In most of the invertebrates, excretory structures are simple tubular forms.

Excretory structures in  vertebrates have complex tubular organs called kidneys.

Protonephridia are primarily concerned with ionic and fluid volume regulation, i.e., osmoregulation.

Protonephridia or flame cells are the excretory structures in Platyhelminthes (Flatworms, e.g., Planaria), rotifers, some annelids and the cephalochordate – Amphioxus.