GWD的一道语法题,, 困惑 which的用法

Although improved efficiency in converting harvested trees into wood products may reduce harvest rates, it will stimulate demand by increasing supply and lowering prices, thereby boosting consumption.
A. in converting harvested trees into wood products may reduce harvest
rates, it will stimulate demand by increasing supply and lowering prices,
thereby boosting.
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.
C. Of converting harvested trees into wood products may reduce harvest
rates, it will stimulate demand by increasing supply and lowering prices,
which boosts.
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.
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.

我在A，B中犹豫，A中it will stimulat 中的it指代不明， B中的which指代什么....答案貌似是B， 照理推的话 which的用法有点迷惑 谁能解释下

A:虽然it可以指代efficiency，但是意思上是不对的。demand是因为增加供给和降价刺激来的，而不是efficiency导致的，efficiency 只是导致了rates的减少。