Barter
a. is the major means of exchange in centrally planned economies.
b. accounts for over 30 percent of the dollar volume of all exchanges in the U. S. economy.
c. entails the exchange of goods for goods.
d. is used to circumvent the problem of a lack of coincidence of wants among potential buyers and sellers.

c. entails the exchange of goods for goods. 

Explanation:

Barter is when goods are exchanged for goods and services are exchanged for services directly, without a medium of exchange.

One of the limitation of the barter system is double coincidence of wants. For example, if Sarah has pens and wants pencils. She has to find someone that has pencils and wants to exchange them for pens. This is double coincidence of wants. It was difficult for people to find people who wanted what they had and had what they wanted. A medium of exchange such as money solves this problem.

Other limitations of the barter system are

1. Lack of store of value

2. Lack of standards for deferred payments

I hope my answer helps you

Barter is no longer a popular means of exchange due to these limitations

answer (b); /// a method of measuring the opinions of a large group of people by selecting a subset of the larger group, asking them a set of questions and then generalizing those responses;