"Bio" Refers to a Gene That Governs a Cell's Ability

"Bio" refers to a gene that governs a cell's ability to synthesize biotin from inorganic precursors. What does the designation "bio⁺" indicate?

A) that the bacterium is biologically inactive
B) that the allele is the mutant allele
C) that the bacterium is biologically active
D) that the allele is normal (i.e., wild type)