Choose the incorrect sentence$(s)$.
$(I)$ $RBCs$ are formed in the white bone marrow in adults.
$(II)$ $RBCs$ have a red colour because of the presence of a protein called haemoglobin.
$(III)$ The nucleus is present in $RBCs$ in most mammals,and they are biconcave in shape.
$(IV)$ $A$ healthy individual has $12-16 \, g$ of haemoglobin in every $100 \, ml$ of blood.

• A
  $I, II, IV$
• B
  Only $II$
• C
  $II, III, IV$
• D
  $I, III, IV$