Answer:
D. 2 cups of flour/1 cup of milk.
Explanation:
Here's the definition of unit rate:
unit rate
the ratio of two different units, with the denominator as 1. For example, kilometer/hour, meter/sec, miles/hour, salary/month, etc.
Since we need to find the unit rate, find the GCF of 6 & 3 (3). Now divide both values by 3.
(6/3)/(3/3)
2/1
The unit rate between cups of flour to cups of milk is 2:1, which is D.