The correct option is B yeast
In Bigo’s distillery the good fermentation vessels contained yellow blobs of cells and bad or the contaminated fermentation vessels contained grey dots of oscillating rods. Louis Pasteur observed that the yellow blobs of cells were responsible for producing alcohol, while the grey dots of oscillating rods in bad fermentation vessels produced lactic acid. Later it was discovered that the yellow blobs were yeast which were responsible for alcohol production, while the grey dots were bacteria that produced the sour-smelling acid.