Step 1: Condition for a pair of lines.
For the equation \( ax^2 + hy^2 + cx + cy = 0 \) to represent a pair of straight lines, the condition is \( a + b = 0 \), where \( a \), \( b \), and \( c \) are constants in the equation.
Step 2: Conclusion.
Thus, the correct answer is \( a + b = 0 \), corresponding to option (B).