Answer: A

Reasoning: The length of isolation for a symptomatic case is based on the period of communicability, not on the incubation period, which instead guides how long exposed but still-well contacts should be quarantined, helps interrupt transmission among contacts, and is used to distinguish secondary from co-primary cases [Kuk, 2005, PMID 16013037; Nishiura, 2009, PMID 18178524].