In Global Economics for Managers, large international banks are identified as the primary and largest participants in the foreign exchange (FX) market, making option C correct. These banks serve as market makers, facilitating currency transactions for governments, corporations, institutional investors, and other financial entities.

International banks dominate FX trading because they possess extensive global networks, large capital reserves, and advanced information systems. They quote buy and sell prices for currencies, provide liquidity, and execute transactions on behalf of clients. Much of the FX market operates through interbank trading, where major banks trade currencies among themselves.

While central banks (option B) are influential participants---particularly through monetary policy and intervention---they do not account for the majority of daily trading volume. Multinational firms and individual traders participate primarily for hedging or speculative purposes, but their transaction volumes are much smaller.

Understanding the role of international banks helps managers assess exchange rate movements, liquidity conditions, and transaction costs in global markets. Therefore, option C correctly identifies the largest participants in the foreign exchange market.