<span>One of the reasons PCB's have been hard to clean up from the puget sound is because they stay in the food chain. Once something is inside an animal it becomes much harder to remove from the environment than if it was just in water.</span>
Answer:
The correct answer is physical boundary.
Explanation:
In my opinion, the kind of boundary it signifies is the physical boundary. The physical boundary is the most general type and is a naturally taking place obstruction in between the two regions due to the existence of either an ocean, river, desert, or mountain ranges. At various occasions, the political boundaries between the states or the countries form along the physical boundaries.