Choose the best answer:
 
‘A’ is a central nervous system structure responsible for reflex actions. It is enclosed within the backbone ‘B’, covered by membranes ‘C’, and gives rise to ‘D’ pairs of nerves.

i. What is ‘A’?
ii. Name ‘B’.
iii. Name ‘C’.
iv. How many nerve pairs are denoted by ‘D’?
 
i. 'A' is .
ii. Bony cage is  
iii. 'C' is .
iii. 'D' is   pairs of spinal nerve.