The the forest reached their highest pricein the 1980s.
products of
productions by
producers to
predictabilities with

The Answer is "products of"

Explanation:

Great question, it is always good to ask away and get rid of any doubts that you may be having.

Based on the sentence that we are working with we can see that it is mentioning price of something. Therefore we can begin to assume that the answer is "products of". Then we can also see that it is also the only one of the 4 options that make grammatical sense when put into the sentence.

So the sentence would be "The products of the forest reached their highest price in the 1980's"

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