Which of the Following Is the Best Example of a Solo

Which of the following is the best example of a solo market exchange?

A) Jimmy buys a new suit from a tailor who visits his office every quarter.
B) Mariah purchases a box of cookies from a store while on vacation.
C) Tommy buys the same brand of toothpaste because he likes the way it tastes.
D) Sunil signs a service contract from a cleaning company.
E) Fred purchases an apartment from his friend who owns a construction company.