Why Do Streptococcus Pneumoniae Colonies on Sheep Blood Agar (SBA)appear

Multiple Choice

Why do Streptococcus pneumoniae colonies on sheep blood agar (SBA) appear like a coin-raised edges and a depressed center?

A) The older growth at the center is smaller due to lack of nutrients.
B) The newer growths on the outside of the colony undergo the Quellung reaction.
C) The older growth at the center is killed due to autolysis.
D) The newer growth has a thicker capsule, therefore it appears raised.