Which of the Following Is a Condition Required for an Exchange

Which of the following is a condition required for an exchange to take place?

A) Each participant must hold on to his or her respective "something of value."
B) Buyers and sellers must be able to communicate about the "something of value" available to each.
C) The items of value offered by the buyers and sellers must be tangible in nature,such as money and cars.
D) Products on offer should be standardized by sellers.
E) Marketers should conduct research to ascertain the need for new goods and services.