Consider five individuals with different occupations.

Mary provides legal advice wants knives sharpened

Clark grows tomatoes wants legal advice

Nathan styles hair wants tomatoes

Polly brews beer wants knives sharpened

Paul sharpens knives wants beer

Which of the following pairs of individuals has a double coincidence of wants?

a$.$

Clark and Nathan

b$.$

Nathan and Polly

c$.$

Mary and Clark

d$.$

Polly and Paul