Question: Foreign Oil Dependency

The important concept here is that mining, manufacturing and agriculture are all nouns. In fact, they are 3 types of industries.

So, we have "By limiting the growth of energy-intensive industries such as NOUN, NOUN and NOUN, and by...."

We have two separate lists.

List 1: By limiting AND by encouraging

List #2: ...such as mining, manufacturing, agriculture

The problem is that list #2 separates the second half of list #1 in such a way that, for clarity sake, we need the second "by" to indicate that we're switching back to list #1.

This is further necessitated by the fact that 2 of the 3 items in list #2 are gerunds (nouns ending in ing) so that it's hard to see that "encouraging isn't part of list #2.

Here's an analogous sentence:

By participating in physical activities such as skiing, running and skating, and eating healthy foods, Marge is certain to live to be 100 years old.

Notice how easy it is to inadvertently add "eating" to the list of physical activities. If we add "by," the sentence is clearer: By participating in physical activities such as skiing, running and skating, and BY eating healthy foods, Marge is certain to live to be 100 years old.

Here's a similar question from the Official Guide: https://gmatclub.com/forum/by-providing-such-services-as-mortgages-home-...