Demand-Pull Inflation occurs when aggregate demand exceeds aggregate supply, causing prices to rise. This statement is correct.
Cost-Push Inflation is caused by an increase in production costs, such as wages and raw materials, which reduces aggregate supply and increases prices. This statement is correct.
Built-In Inflation, also known as Wage-Price Inflation, occurs when workers expect future inflation and negotiate higher wages, which raises production costs and further fuels inflation. This statement is correct.
Therefore, all statements I, II, and III are correct.