As municipal water experts very well know, successive years of greater than average rainfall can lead to dramatic surge of water usage, with the populace ______________ the very habits that had once sustained the city through its drought years.

a) Engaging in
b) Returning to
c) Altering
d) Mocking
e) Relying on

As you can tell, this sentence, or this text completion, is nowhere near as simple or straightforward as the text completion you saw in the example of the elimination method example.

Therefore, it's far more indicative of what you're going to see on the actual GRE. That is, you're going to be dealing with some pretty long convoluted sentences. So, what must we do?Well, first thing to do is to break down long sentences in your own words.
After reading through the entire sentence it is clear that there is a lot going on here, but you want to take apart the sentence and focus on the main part.
So, experts may very well know, that's fine. What are they knowing, though? That's the important part. Greater than average rainfall. Let's just call that greater rainfall, can lead to a surge, which means an increase in water usage.

So, lots of rain, water usage goes up. Notice how I'm using my own words now? That's breaking down the sentence. Why am I using my own words? Because it makes it easier for us or easier for the person breaking down the sentence to conceptualize what the sentence is about, instead of trying to use GRE's words.Going back to our sentence here--again, there's lots of rain, then water usage increases, or more people use water. So, we got to that part where the comma is. Now, we will read on. With the populace, blanking the very habits that had once sustained the city though its drought years.

So, this part says the people, the populace, they're doing something to the habits. What? Well, let's read on. Blanking the habits that had once had sustained the city, so the sustained means to keep something going.

Their habits help the city through their drought years, so years where there was little rain. So when there's little rain, well, what are people doing in terms of habits? Well, people are not using a lot of water.

So do you see how if you break down the second part, you realize that the population--well, what are they doing to their habits, to their drought habits? Well, drought habits are or is using little water, whereas when there's lots of rainfall, people use lots of water.

So,what do they do to these drought habits? They change them, or they drop them, something to show that they're no longer doing these habits. They are no longer engaging in these habits, and notice here if I look down at 'A', it's there waiting to trick me, but I'm not going to let it do that.

Again, what do we do? Well, we come up with our own word. So again, in a long sentence like this, we break down the sentence. We look for these clues scattered throughout; clues that kind of give us a meaning, and then we put in our own word.

Evaluating the options

If you plug in words, words like "engaging in" can suddenly make sense. Why? Because you haven't really broken down the sentence, and so, you're likely to misinterpret the sentence, but we know that "engaging" doesn't mean to change or changing.
We're turning to the very habits. Well, wait a second. If the population is changing their habits during heavy rainfall, changing their drought time habits, they're definitely not returning to them, and there we have C, which is "altering." Just like that, we matched, and it doesn't always have to be a perfect match.
Maybe 'altered' wasn't your word. Maybe you came up with another word that's similar to change. I earlier said dropping the very habits, but the idea is that it should be a similar word or very similar word, and that's the answer.

Mocking doesn't make sense. In the terms of you mock something, you make fun of something, so they're not making fun of the habits, nor are they relying on their drought time habits.

They again are changing them, so that now they are using lots of water. Just like that, we've broken down the sentence, looked at the scattered clues, put together a unified meaning, come up with their own word, matched, and there's our answer.