The "unit rate" is the rate having 1 unit in the denominator:
C. 30 miles per hour
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Usually a "unit rate" is one with different units in the numerator and denominator. Selection B has one unit (day) in the denominator, but both numerator and denominator are time units. The value of B is 7/24, a "unitless" quantity. It is unitless because the time units (hour/hour) cancel, leaving no units.
