Commodities are
a. trade rules.
c. goods with value for trade.
b. methods of transportation.
d. coins

Commodities are goods with value for trade. the correct option as far as the given question is concerned is option "c". There is definite requirement of certain typers of precious or important goods to trade with other people. This trading can take place between two persons having valuable commodity or in exchange for coins. The barter system was prevalent in the years gone by. This allowed two people to exchange valuable goods during trading. Later on with the advent of coins the trading took place by exchanging coins with precious goods.

Main idea on left, details on right