To solve the inequality \( a - 12 < -20 \), we start by isolating \( a \).
- Add \( 12 \) to both sides of the inequality: \[ a - 12 + 12 < -20 + 12 \] This simplifies to: \[ a < -8 \]
So the solution to the inequality is \( a < -8 \).
The correct choice is:
A. \( a < -8 \).