A cycle of expansion and contraction phases that a nation's economy experiences over time is .

The business cycle model shows the fluctuations in a nation's aggregate output and employment over time. The model shows the four phases an economy experiences over the long-run: expansion, peak, recession, and trough.

Explanation:

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The business cycle model shows the fluctuations in a nation's aggregate output and employment over time. The model shows the four phases an economy experiences over the long-run: expansion, peak, recession, and trough.

Explanation:

we need the diagram to answer this correctly.