Help please! Which is the correct biochemical sequence in the pathway for synthesis of the amino acid arginine?

a) ornithine is converted to arginine, which is then converted to citrulline

b-) citrulline is converted to arginine, which is then converted to ornithine

c-) arginine is converted to citrulline, which is then converted to ornithine

d-) ornithine is converted to citrulline, which is then converted to arginine