D) increasing the number of fish that live in the river.
Pollution will lead to the death of fish, decreasing their numbers. 
Hope that helps!
        
                    
             
        
        
        
The economic term is the opportunity cost.
The concept of opportunity cost is a relatively inexpensive and relative measure that involves people's preferences, so it varies from person to person. It is a question of comparing what is left over when making a decision.
In Katie's case, the opportunity cost of the money she saves to buy a car is what she fails to do with that money. For example, she stops investing in stocks, fails to make a trip, etc.
All decisions involve an opportunity cost. Taking another example, the opportunity cost of studying for the test at the end of the week is measured by the loss of leisure you would have. However, the decision to study for the test is chosen because it is more valuable.
 
        
                    
             
        
        
        
The second amendment gives people the right to bear arms.
        
                    
             
        
        
        
Answer:
d
Explanation:
stages 1-4 of sleep or "quiet" sleep where brain functions are suppressed, sleep thinking occurs, the REM-off neurons secrete setotonin and norepinephrine, new episodic memories are enhanced, select neuronal connections are weakened, and sleep walking/talking (deep sleep) occurs
REM sleep deprivation results in a REM rebound
 
        
             
        
        
        
The mountain and its risk It will depend on the type of mountain to climb, and the season of the year...
Mountaineering techniques vary greatly depending on location, The everest is very different compare to The Aconcagua, also season, and the particular route a mountaineer chooses to climb. 
Mountaineers train to climb on all types of terrain whether it be snow, glacier, glacial Ice, water ice, or rock. The challenges appear in all different kinds.
Each type of terrain presents its own hazards. Always Safety is first. Climbers must be skilled in dealing with the different challenges that could arise from different terrain.