Step 1: Understanding the Concept:
This question tests knowledge of a specific idiomatic construction used for making comparisons of degree or method.
Step 2: Detailed Explanation:
The correct idiom for this type of comparison is "not so much X as Y." It is used to say that Y is a more accurate description or cause than X. For example, "He succeeded not so much by talent as by hard work."
The structure requires parallelism between X and Y.
In the original sentence:
X = "by aggressive marketing"
Y = "by networking and word of mouth"
The two phrases starting with "by" are parallel. The idiom "not so much by... as by..." is used correctly. Therefore, the original sentence is correct.
Let's look at the other options:
(B) "As much with... as with" is not the correct idiom.
(C) "Much by... that instead by" is ungrammatical.
(D) "So aggressively with... but with" is not the correct idiom.
(E) "In... but rather in" is a different construction and not as precise here.
Step 3: Final Answer:
The sentence uses the standard, correct, and parallel idiom "not so much by [something] as by [something else]." The original wording is the best choice.