If you were to design an experiment to test whether a particular pathogen caused a disease, which of the following choices would be the first step and which the last step you would make if you followed the scientific method precisely?

Smallpox vaccine, the first successful vaccine to be developed, was introduced by Edward Jenner in 1796. He followed up his observation that milkmaids who had previously caught cowpox did not later catch smallpox by showing that inoculatedcowpox protected against inoculated smallpox.

Where are the options?