Instructions: You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.
Input: In the 18th century, smallpox was a common and deadly disease. A country doctor, Edward Jenner, observed that patients working with cattle who contracted a mild disease called cowpox, never came down with the more serious smallpox. When Jenner obtained liquid from cowpox sores and injected it into healthy patients, they became immune to smallpox. What term best describes Jenner's treatment for smallpox?
(A) vaccination (B) gene therapy (C) chemotherapy (D) genetic engineering
Output:
A