Gastronome : food : :

a.
writer : exercise

b.
mechanic : car

c.
carpenter : computer

d.
nurse : horse

B. Mechanic : Car

Explanation: Like gastronome is the analogy of food as the gastronome is the lover of food, similarly Mechanic is however not necessarily the lover of cars but the one who's into the business of repairing and dealing with them regularly and thus, somehow has an association towards them. A writer can be a lover of books or pens but not exercise, neither can the carpenter have a love for the computer or the nurse would have for a horse as compared to the affinity that the mechanic has for cars. Thus, this provides us the answer.

i think it could possibly be b