The diagram below shows a shift in an economy's short-run aggregate supply curve from SRAS1\text{SRAS}_1SRAS1 to SRAS2\text{SRAS}_2SRAS2, while its classical long-run aggregate supply curve (LRAS\text{LRAS}LRAS) remains unchanged at the full-employment level of output, YfY_fYf.
Which of the following events is the most likely cause of the shift shown in the diagram?
A sustained increase in labor productivity due to state investment in training programs
A significant decrease in the nominal wage rate across major industries
A sharp increase in the global price of imported industrial raw materials
An expansion of the country's capital stock through net private investment