The question says that the airplane manufacturer reduced the hazardous waste output from 90 tonnes/worker to 40 tonnes/worker. How can this ratio (tonnes/worker) be decreased? It can be decreased if the actual emissions decrease but the number of workers remain the same or decreases (i.e. the numerator decreases in greater proportion to the denominator). Alternatively, it can be decreased if the number of workers goes up, but the emissions stay the same or increase less in proportion to the increase in the number of workers (i.e. the denominator increases in greater proportion to the numerator).

In the first case (emissions going down), the airline manufacturer would have actually reduced emissions. In the second (number of employees going up), the ratio would decrease without the emissions necessarily going down. Therefore, for this to represent a true decrease in emissions, we will have to assume that the number of employees did not go up.

Option (E) expresses this most clearly and is therefore the best choice.

Answer: E