Which of the following best defines variolation as it was historically practiced for smallpox?

Deliberate inoculation of healthy people with material from smallpox lesions to induce immunity

Injection of a cowpox extract that contains only isolated proteins to elicit a focused immune response while avoiding transfer of full infectious virus particles

Administration of a chemically weakened smallpox virus produced in laboratory cell culture under sterile conditions to generate immunity without disease

Genetically engineering a related but nonvirulent virus to express smallpox antigens and then giving it to people to trigger long-lasting protective immunity