Which of the following is equivalent to a quart?

A quart is a unit of volume measurement in the customary system, equivalent to two pints or four cups. When looking for an equivalent measure, it's essential to recognize that the term "quart" itself refers to the standard unit, meaning it will always equate to itself.

In the context of the other options, a pint is a lesser volume (1 quart = 2 pints), a liter is a different metric volume that is close but not equal (1 quart ≈ 0.946 liters), and a gallon represents a larger volume (1 quart = 0.25 gallons). Therefore, the only option that accurately and directly equals a quart is a quart itself.