Final Answer:
The substance that must be formed first before A or B specificity is determined is .I.Thus option c is the correct option.
Step-by-step explanation
Determining the specificity of A or B blood types involves understanding the presence or absence of certain antigens on the surface of red blood cells. These antigens are inherited from our parents. The A, B, and O blood types are determined by the presence or absence of antigens A and B, along with another factor, the Rh factor (positive or negative).
Now, let's break down the options. Bombay blood group is a rare blood type where individuals lack both A and B antigens, resulting in the O blood type appearance. However, for the specificity of A or B to be determined, the presence or absence of the I substance, also known as the H antigen, is crucial. This H antigen serves as a precursor for the A and B antigens. Individuals with the Bombay blood group lack the H antigen, and without the H antigen, A or B specificity cannot be established.
In conclusion, the formation of the H antigen (C. I.) is the initial step in determining the A or B specificity, as it acts as the foundation for the subsequent development of A and B antigens. Therefore, the correct answer is C. I.
Therefore option c is the correct option.