An Epidemiologic Survey of Roller-Skating Injuries in Metroville, a City

An epidemiologic survey of roller-skating injuries in Metroville, a city with a population of 100,000 (during the midpoint of the year) , produced the following data for a particular year:
Number of skaters in Metroville during any given month: 12,000
Roller-skating injuries in Metroville: 600
Total number of residents injured from roller-skating: 1800
Total number of deaths from roller-skating: 90
Total number of deaths from all causes: 900
The proportional mortality ratio (%) due to roller-skating was:

A) 90/600 × 100.
B) 90/100,000 × 100.
C) 90/1800 × 100.
D) 90/900 × 100.