When Performing the O/F Test, One Tube Is Covered with Mineral

Multiple Choice

When performing the O/F test, one tube is covered with mineral oil and one tube is left uncovered. Why is one tube covered with mineral oil?

A) To create an anaerobic (fermentative) environment
B) To create an aerobic (oxidative) environment
C) To create a reductive environment
D) To create an asaccharolytic environment