Reference example:

1, why is there a decline in enrollment during the economic downturn?

Why is there an enrollment bubble in the current economic downturn?

Throughout American history, during wars, economic recession and immigration, economic growth was sometimes good and sometimes bad.

Throughout American history, national development has experienced ups and downs in wars, economic recession and immigration.

After losing their farm in the recession, the family moved to Portland.

After losing their farm in the recession, the family moved to Portland.