A Strain of Neurospora Is Able to Grow on Minimal

Multiple Choice

A strain of Neurospora is able to grow on minimal medium.When substance A is added to the medium, however, the strain cannot grow.Supplying a small amount of substance B has no effect on the strain, but it cannot reverse the effect of substance A.Supplying a small amount of substance C, by contrast, enables the strain to grow with substance A.Which of the following statements best explains these facts?

A) Substance A is a toxin that the strain cannot break down, and substance B is an enzyme that breaks down substance A.
B) Substance A is a toxin that the strain cannot break down, and substance C is an enzyme that breaks down substance A.
C) The strain has the capacity to produce substance C.
D) Substance A is a mutagen.
E) Substance C is a mutagen.