Answer:
C. 2.5 days/mi
Step-by-step explanation:
Speed is defined as the distance covered by an object divided by the time taken to cover that distance:
where
S is the distance covered
t is the time taken
At the numerator of the fraction, we have distance, which is a lenght. Lenght is measured in different possible units: meters (m), kilometer (km), mile (mi), centimeter (cm)...
At the denominator, we have a time, which can be measured in seconds (s), minutes (min), hours (h), days..
According to this, we can see that option
C. 2.5 days/mi
cannot represent a speed. In fact, at the numeratore we have days (which is a measure of time), while at the denominator we have mile (which is a measure of length), so in this fraction distance and time are inverted, therefore this cannot be a measurement of a speed.