Final answer:
Cattle receive the greatest percentage of the anthrax vaccine due to their high risk of exposure to the bacterium Bacillus anthracis, which causes anthrax (option d).
Step-by-step explanation:
The mammal population that receives the greatest percentage of the anthrax vaccine due to being at the highest risk of contracting the disease is d) Cattle. Anthrax primarily impacts animals traditionally involved in agriculture such as sheep, goats, cattle, and deer, and the vaccine is administered to mitigate this risk. In particular, cattle are at significant risk due to their close contact with humans and the frequency with which their animal products are used. While the anthrax vaccine is not routinely administered, it is given to certain at-risk adult populations, including some individuals working directly with animals or their products.
Hence, the answer is option d.