Hello!
To solve this exercise, let's think a bit and choose the best option for each alternative.
(a) Karen's desk is about 3...
Well, a desk with 3mm or 3cm is too small, and with 3km is too big.
In this case, the best option is 3 meters (even though it's big, it's the best option).
(b) Dan's refrigerator has a mass of 80...
Usually, a refrigerator is heavy. So the best option is kilograms.
(c) The bucket holds about 5... of water.
5ml of water is too little, it fits in a spoon. The correct option is liters.
Answers:
a. meters
b. kilogr