rrsnathan
John,a resident of Lake City and an employee of The Bell Company,is currently working on a new project that will revolutionize the telecommunication industry, which will lead to a lowering of rates for making international calls.
A)is currently working on a new project that will revolutionize the telecommunication industry,which will lead to a lowering of rates for
B)is currently working on a new project that will revolutionize the telecommunication industry,leading to a lowering of rates for
C)which is currently working on a new project to revolutionize the telecommunication industry and also lead to a lower rates for
D)who is currently working on a new project in the telecommunication industry,which will lead to a lowering of rates for
E)has been currently working on a new project that will revolutionize the telecommunication industry as well as lower the rates for
This is a fun one! We have some easy splits for these answer choices, making it quite easy to narrow in on the correct answer.
First and foremost, get rid of that modifying phrase separating the main subject and the main verb:
"John,..., ..."
Looking at the answer choices we can either have a verb or a clause after our main subject. Let's look at the answer choices with "which" and "who" to see if we get a suitable main verb later in the sentence. Well answer choice (C) doesn't work since it is one long clause and no main verb appears at the end. Answer choice (D) is even worse. It just adds another clause to the end of the first clause. So both of these answer choices fail since there is no main verb.
Now we are left with answer choices that contain a main verb. Answer choice (E) stands out for not being a simple verb tense. Anytime have a verb tense, I check the sentence to see if we are dealing with more than one period of time. In this sentence, we are not trying to establish different time periods for an event so I quickly toss this answer choice out.
Alright, phew! When I make it to two answer choices, I know things are going well and I am getting close. But I also know that this is when I really need to focus and pay attention to the subtleties of the sentence. No more easier throw aways. So what is the major difference between (A) and (B)? Well, it comes at the end. Do we need to create a "which" clause or can we merely have a participle phrase. Well, in this case since we have a "that" clause immediately preceding this part of the sentence, a "which" clause is a little suspect. The modification of the preceding noun is too far away. Whereas if we use a participle phrase, then we can easily convey the result of the "project." Furthermore, with the participle phrase, we have a more concise construction that avoids extra verbiage, such as "will lead." Always side with the more concise construction. Thus, we have our answer!

I hope this helps!