Dr Edward Jenner Realized That Cows Have a Disease Called

Dr. Edward Jenner realized that cows have a disease called cowpox, which is like a disease that infects humans called smallpox; Jenner noticed that milkmaids who hands were infected with cowpox were not contracting smallpox. Jenner infected a child with the pus from a cowpox blister, and found that the child did not contract smallpox. Which statement represents a supporting hypothesis?

A) The cowpox virus prevented the small pox virus from entering the child's immune system.
B) The smallpox virus was so similar to the cowpox virus that the child's immune system recognized it and was able to fight it.
C) The cowpox infection will prevent the child from being infected by the small pox virus.
D) The cowpox infection will have no affect on the child's immunity to the small pox virus.