According to classical economic theory, as exemplified in Adam Smith’s Wealth of Nations, published in 1776, the market is self-regulating and achieves equilibrium when it is free and without government intervention. He said that market forces are an invisible hand and that supply and demand, when free, are based on rational choices that automatically keep them at equilibrium. Self-interest on the part of both consumers and suppliers results in maximum utility and maximum profit, and resources are allocated on this basis. The equilibrium is achieved through competition among suppliers to attract consumers. This invisible hand of supply and demand determines equilibrium for the production and price of goods and for the distribution of income.
John Maynard Keynes developed his economic theories during the Great Depression of the 1930s. In 1936 he published The General Theory of Employment, Interest and Money. This theory states that the market economy tends to be unstable and volatile, which leads to recession and inflation. To minimize this, governmental action is needed in monetary and fiscal policy to restore equilibrium.
Therefore, in regard to your question, the correct answer is b. Keynes did not believe the market was always in equilibrium; the classical economists did.