Explanation

Cow milk proteins are primarily casein (approx. 80%) and whey protein (approx. 20%). Among whey proteins, alpha-lactalbumin is the most abundant, making up about 40-50% of the whey fraction, whereas beta-lactoglobulin makes up about 50% of whey in some species but is absent or low in human milk; however, in cow milk, alpha-lactalbumin and beta-lactoglobulin are both significant, but standard veterinary/food science texts often cite alpha-lactalbumin as the major specific whey protein or note that casein is the absolute maximum. Wait, let's re-verify. Actually, casein is the maximum overall. If the question implies whey proteins specifically, beta-lactoglobulin is often cited as the most abundant whey protein in cow milk (approx 50% of whey), while alpha-lactalbumin is approx 20%. Let me double-check standard MCQs for this exact phrasing. Many sources say 'beta-lactoglobulin' is the major whey protein in cow milk. However, some older texts or specific contexts might say alpha-lactalbumin. Actually, beta-lactoglobulin constitutes about 50% of the total whey proteins in cow milk, while alpha-lactalbumin is about 20%. So A is likely correct for whey proteins. But the question says 'Milk proteins... contains maximum amount'. Casein is not an option. Among the options, beta-lactoglobulin is indeed the most abundant whey protein in cow milk. I will stick with A as it is standard for this specific MCQ found in Pakistani exam banks (e.g., FPSC/PPSC).