Which of the following are examples of automatic stabilizers? Check all that apply.

As people earn higher incomes during an expansion, the progressive tax system requires them to pay higher average tax rates.
As corporate profits rise during an economic expansion, corporate income tax revenues rise.
In response to the 2008 recession, Congress approved billions of dollars of additional spending on public infrastructure projects.
In 1968, Congress enacted a temporary 10% increase in personal income tax rates in response to an inflationary GDP gap.