It says “identify the population , the units , & each variable. Then tell if each variable is categorial or quantitative.”

The choices can be found elsewhere and as follows:

a. an understanding of significant figures in metric units 
b. an understanding of the difference between accuracy and precision of units 
c. an equality that tells how much of one unit is equal to another unit 
d. an algebra book that explains how linear equations can be set up with units

I believe the correct answer is option C. The important thing in this conversion is an equality that tells how much of one unit is equal to another unit.