When jenner developed the first vaccine he was using the observation of milk maids who]

Who became immune to smallpox after getting infested by cowpox.

Explanation:

A successful vaccine for smallpox was developed by Edward Jenner in 1796. He used the observation of milkmaids who became immune to smallpox after getting infected by the cowpox virus. It is due to the fact that the virus, which leads to cowpox infection is identical to the smallpox virus. When the milkmaids got infected by the cowpox virus, their immune cells generated antibodies, which can also destruct virus for smallpox, and therefore, they were not affected by the smallpox virus.

humans are now responsible for causing changes in the environment that hurt animals and plant species. we take up more space on earth for our homes and cities. we pollute habitats. human activity often changes or destroys the habitats that plants and animals need to survive.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.