We _____ thousands of trees if trees if we _____ paper. A. save / waste B. will save / won't waste C. will save / don't waste D. won't save / don't waste

The correct answer is B. will save / won't waste. This sentence is a conditional sentence in the future tense. The first part of the sentence states the condition ("if we waste paper"), and the second part states the result ("we will save thousands of trees"). In this case, we use "will" to indicate future action and "won't" to indicate negation.