If sin x + a cos x = b, then what is the expression for |a sin x - cos x| in terms of a and b?

• A. \(\rm \sqrt{a^2-b^2-1}\)
• B. \(\rm \sqrt{a^2+b^2-1}\)
• C. \(\rm \sqrt{a^2+b^2+1}\)
• D. \(\rm \sqrt{a^2-b^2+1}\)