Answer:
3 books for 2
Step-by-step explanation:
A unit rate is the amount of something for one singular unit, therefore the last one is not a unit rate.
Answer: 3 books for 2.
Since a unit rate is a comparison of a number to 1,
There is no comparison to 1 at all in 3 books for 2.
Therefore, your answer is concluded to be 3 books for 2.