gwd 6-16

Q16:

Not only did the systematic clearing of forests in the United States create farmland (especially in the Northeast) and gave consumers relatively inexpensive houses and furniture, but it also caused erosion and very quickly deforested whole regions.

1. Not only did the systematic clearing of forests in the United States create farmland (especially in the Northeast) and gave consumers relatively inexpensive houses and furniture, but it also
2. Not only did the systematic clearing of forests in the United States create farmland (especially in the Northeast), which gave consumers relatively inexpensive houses and furniture, but also
3. The systematic clearing of forests in the United States, creating farmland (especially in the Northeast) and giving consumers relatively inexpensive houses and furniture, but also
4. The systematic clearing of forests in the United States created farmland (especially in the Northeast) and gave consumers relatively inexpensive houses and furniture, but it also
5. The systematic clearing of forests in the United States not only created farmland (especially in the Northeast), giving consumers relatively inexpensive houses and furniture, but it

答案是b，我觉得要是b的话，句子不就没有主语了么？

这题a,b是倒装

主语是The systematic clearing of forests