The Diagram Below Shows the Urinary Metabolic Ratio as a Measure

The diagram below shows the urinary metabolic ratio as a measure of CYP2D6 enzyme activity in a total of about 700 individuals. After individuals were given a standard dose of a drug known to be metabolized by CYP2D6 the metabolic ratio was obtained by measuring the urinary concentration of the substrate drug and dividing it by the concentration of the metabolic product resulting from CYP2D6 acting on the drug. Classify individuals with metabolic ratios in the four ranges shown as (a) to (d) in terms of their drug-metabolizing abilities and describe the expected genotypes associated with each group.