Answer:
D. Trad-able emissions permit.
Step-by-step explanation:
When a city is able to buy and sell the rights to this total discharge level with other cities, then it is called as trad-able emissions permit. Trad-able emissions permit are well used for controlling the emissions and thereby the overall pollution is also controlled. It also provides permission for an industry or city to pollute in a controlled amount for a given time period.