I've found a wrinkle: 8)

By providing x,y,z, and by staying within the limits, the company remained profitable.

Which is it?

parallel form:
by staying within the limits

or Ellision form:
By providing x,y,z and staying within the limits, the company remained profitable.

Question: When is parallel form required vs. elision form: omit the adjective

thanks much,
mww7786

Mww,

The question you cite in the Official Guide is a fantastic example of what parallelism means on the GMAT.

In the question, there are 4 elements that are meant to be parallel as "services":

1. mortgages
2. home improvement loans
3. automobile loans and
4. financial advice

The fifth element, "staying within the metropolitan areas" is clearly NOT parallel to the 4 listed above. Logically, staying within the metropolitan areas is not a service in the same way as mortgages, etc.

As a result, the fifth MUST be treated differently and set off from the prior list. Therefore, you would require a "by" or something similar to indicate that the fifth element was not simply the fifth of a list of logically identical elements.

By the same token, the end of the list of 4 elements must be noted with an "and" before the 4th element.

Therefore, the correct answer is, as noted, answer choice (E).

I hope that this is helpful. - Andrew