Teacher:In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").
Teacher: Now, understand the problem? Solve this instance: Fact1: Active immunity results when an immune response to a pathogen produces memory cells., Fact2: Memory cells persist in the circulation for decades., Question: what can persist in the circulation for decades? (A) active immunity (B) density (C) Veins and arteries. (D) oxygen cells (E) bacteria (F) chlorofluorocarbons (G) fur and fat (H) Chemical energy
Student:
A