The correct answer is B (12) because the degrees of freedom for a chi-square test of independence in a contingency table are calculated as $(r - 1)(c - 1)$, where $r$ is the number of rows and $c$ is the number of columns. Here, $r = 5$ and $c = 4$, so the degrees of freedom are $(5 - 1)(4 - 1) = 4 \times 3 = 12$.

• Option A (7) is incorrect as it results from using the formula $r + c - 2$, which is not applicable here.
• Option C (20) is incorrect as it arises from omitting the $-1$ adjustment, leading to $r \times c = 5 \times 4 = 20$, which is not the correct calculation.