Go through the following flow chart for division of subphylum vertebrata. Fill the gaps A, B, C and D and select the correct option.

Subphylum Vertebrata is divided Into two divisions. They are agnatha (jawless) and gnathostomata (with jaw). Agnatha are further divided into two classes-Ostracodermi, which is extinct and Cyclostomata (e.g., hag fish). Jawed vertebrates are divided into two superclasses-Pisces (true fish) and Tetrapoda (four limbs).