If (x - k) is the HCF of x2 + ax + b and x2 + cx + d, then what is the value of k?

• A. \(\frac{{d - b}}{{c - a}}\)
• B. \(\frac{{d - b}}{{a - c}}\)
• C. \(\frac{{d + b}}{{c + a}}\)
• D. \(\frac{{d - b}}{{c + a}}\)