"km" is used to measure the length of the soccer field.
Step-by-step explanation:
There are so many units to measure the length of an object. We wish to tell that out of 4 units in the given options, which will we use to measure the length of a soccer field.Out of 4 options, mm is smallest unit while km is the biggest unit.A soccer field is big in size, it means that km is used t measure the length of a soccer field.So, the correct option is (d) "km".