The yellowstone national park food web is shown below

Option D

Explanation:

in this food chain, it is clear that gray wolf feed upon Moose and the moose feed upon following primary food resources - a) Maple b) Balsam Fir c) Aquatic plants and d) cotton wood. Except Balsam, there are other organisms as well who are feeding upon Maple and Aquatic plants.  

Therefore, any change in balsam plants population is directly affected by change in population of Mouse.  

Now if the population of gray wolf is increased, they will feed upon mouse and hence the balsam fir will flourish to its full extent as the population of its only primary consumer i.e mouse will decrease.  

Hence, option D is correct

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explanation: