Refer to the Graph Showing a Person's Immune Response, First

Refer to the graph showing a person's immune response, first to a vaccination, and later to exposure to the pathogen that the vaccine targeted.Time is represented on the x-axis, but the scale is different for each subdivision. If the graph shown represents a time course following a person's vaccination against measles, which is an accurate estimate of times labeled A-D?

A) A must be months; C must be weeks.
B) A must be weeks; B could be days to years.
C) A must be days; D must be years.
D) B must be months; D must be years.
E) C must be months; D must be years.