The genes a bacterium uses to produce the amino acid arginine form part of the arg operon.  In this operon, when arginine binds to the repressor protein, transcription of the structural genes of the arg operon is blocked.  What type of operon is the arg operon?

A.   An inducible operon

B.   A repressible operon

C.   A catabolite operon

D.   The genes are constitutively expressed

 (i)   Which response (A-D) is the best choice? (1 mark)

(ii)  Briefly explain your reasoning for your choice (2 marks)