Krissy predicted that she would sell 65 sweaters. She actually sold 85 sweaters. What are the values of a and b in the table below?

Item: sweaters
Approximate value: 65
Exact value: 85
Error: a
Absolute error: b
Ratio: ( blank )
Percent error: ( blank )
A a = negative 20; b = negative 20
B a = negative 20; b = 20
C a = 20; b = negative 20
D a = 20; b = 20