Pick A
B. In converting harvested trees into wood products may reduce harvest rates, demand will be stimulated because of increasing supply and lowering prices, which boost.
Passive voice is used. Unclear reference of "Which".
C. Of converting harvested trees into wood products may reduce harvest rates, it will stimulate demand by increasing supply and lowering prices, which boosts
"prepositional error"(" of "instead of "in"). Unclear refrence of "which". "boosts" is singular preceded by "compound" subject.
D. Of harvested trees being converted into wood products may reduce harvest rates, it will stimulate demand, because it will increase supply and lower prices, thereby boosting.
Awkward Sentence construction. USage of "being" shoule be way easy to eliminate..
E. When harvested trees are converted into wood products may reduce harvest rates, demand will be stimulated because of increasing supply and lowering prices, which boost.
Passive voice construction.
Pick A for clear meaning. "it" refers back only to "efficiency". Efficiency is singular and "it " refers back to singular subject/noun.