Yard is to inch as quart is to

In a word analogy of the form A : B :: C : D, the relationship that connects A and B must also connect C and D. Yard and inch are both units of the same kind of measurement (length), and a yard is the larger unit (1 yard = 36 inches), so the governing relationship is: a larger unit of a given measurement paired with a smaller unit of that same measurement.

A quart is a unit of volume. Applying the same larger-to-smaller relationship, the answer must be a smaller unit of volume. Here, ounce refers to the fluid ounce (the volume unit, not the weight/mass unit of the same name): a quart equals 32 fluid ounces in the US customary system (40 in the imperial system), so a fluid ounce is a much smaller unit of volume than a quart either way — this exactly mirrors inch being a smaller unit of length than yard.

• gallon: a gallon is larger than a quart (1 gallon = 4 quarts), which reverses the required larger-to-smaller direction, so it fails the relationship.

• milk: milk is a liquid substance, not a unit of measurement at all, so it cannot complete a units-based analogy.

• liquid: liquid names a state of matter, not a specific unit of measurement, so it also fails to fit the pattern.

Only ounce is a smaller unit of volume than a quart, so it completes the analogy while keeping the same larger-to-smaller relationship as yard is to inch.