A software system checks age in order to determine which welcome screen to display.

 A correct list of boundary values for the age input should include the minimum and maximum values of each age group (0, 12, 13, 18), as well as the values just below and above each boundary (-1, 19). Boundary value analysis is a test design technique that involves testing the values at or near the boundaries of an input domain or output range, as these values are more likely to cause errors than values in the middle. Option A satisfies this condition, as it has all six boundary values (-1, 0, 12, 13, 18, 19). Option B has two values from the same equivalence class (12 and 13), option C has only four boundary values (0, 12, 18, 19), and option D has no boundary values at all. Verified References: A Study Guide to the ISTQB® Foundation Level 2018 Syllabus - Springer, page 34.