In the B.C.G. vaccine, the word `C` stands for Calmette. The B.C.G vaccine is used to prevent tuberculosis (TB) and is named after the French scientists Albert Calmette and Camille Guérin who developed it. The vaccine is composed of live tuberculosis bacteria that have been weakened or attenuated. When administered to individuals, it elicits an immune response that protects against TB infection. The `C` in B.C.G. is a tribute to Albert Calmette, who played a critical role in its development. Therefore, option 1, Calmette, is the correct answer. It is important to note that options 2, 3, and 4 (Cough, Chlorine, and Cadmium, respectively) are not valid explanations for what the `C` stands for in the B.C.G. vaccine.