Most bacteria prefer to use glucose as a carbon source. However, if glucose is not available, the bacteria can use the sugar lactose as a carbon source instead. In order for bacteria to use lactose, they must make an enzyme to break down the lactose. This enzyme is called lactase. If there is no lactose, the bacteria will not make the enzyme. This production of lactase is an example of -
A. cellular respiration in prokaryotes
B. genetic variation between organisms
C. an organism adapting to its surroundings
D. regulation of gene expression