Answer: Option D
In order for exchange to occur each party must have something of value to the other party. For an exchange to happen, both parties have to have something of value for each other. For instance, a man visiting a coffee shop might have enough money to buy a cup of coffee while the cafe has the coffee. Both parties must be able to communicate with each other, and both must want to exchange something and be able to do so. If the customer in the coffee shop can't make himself understood, or if he decides he doesn't want a cup of coffee, or if he turns out not to have quite enough money, then there will be no exchange. If all of the needed conditions are met, there will be an exchange of money for coffee.