A local Birmingham-area restaurant chain introduced a new summer menu in its Vestavia Hills location, but not its Mountain Brook location.Nightly revenue averaged $6,000 in Vestavia Hills and $4,000 in Mountain Brook before the menu change, but $7,000 in Vestavia Hills and $3,000 in Mountain Brook after the menu change.The difference-in-difference estimate of the increase in average nightly revenue attributable to the menu change is

$4,000.

$0.

$1,000.

$2,000.