(A) Incorrect.

Let me first discuss a variation of this option:

A’: Residents will reduce the amount of trash they put out for collection

Is A’ an assumption?

I don’t think so. Let me explain.

The argument says that X (charging each household for the trash it generates) will lead to Y (reduction in the amount of residential trash). Thus, X will help.

A’ says that Y will happen.

Think about it. I say, “X will lead to Y. Thus, X will help.”

Am I assuming that Y will happen? (“Y will happen” means there are no conditions attached to the occurrence of Y. This means that Y will happen, irrespective of X.)

No.

Am I assuming that X will make Y happen?

I don’t think so. I’m directly stating, “X will lead to Y.” How can a rephrasing of my statement be an assumption? It’s not.

From the above discussion, we understand that “Residents will reduce the amount of trash they put out for collection” is not an assumption of the above argument.

Now, let’s look at the original option A:

Residents will reduce the amount of trash they put out for collection by reducing the number of products they buy.

The option says that the residents will reduce the amount of trash in a specific way. Which way? By reducing the number of products they buy.

Does it matter to us how they reduce the amount of trash?

Not at all. 

Whether they reduce the number of products or shift to using only those products that produce less trash is none of our concern.

Thus, option A is incorrect.

(B) Incorrect. 

This option weakens the argument; the option indicates that the collection fee may fail to reduce the amount of trash the residents put out for collection.

Since this option weakens the argument, it cannot be an assumption.

(C) Correct. 

This option strengthens the argument by saying that the collection fee will not lead to dumping of trash in the parklands.

On negation, the option says:

The collection fee will induce residents to dump their trash in the parklands illegally.

In this case, the argument falls flat since if the collection fee induces residents to dump their trash in the parklands illegally, charging the collection fee will not save the parklands.

Since the argument breaks down on negating the option, option C is an assumption.

(D) Incorrect. 

This option has no impact on the argument. Whether the beauty of the parkland is an important issue or not for the residents doesn’t help us evaluate whether charging the collection fee will reduce the amount of trash residents generate or not.

(E) Incorrect. 

This option has NO IMPACT on the argument. Our concern is whether charging households a fee for the amount of trash they generate will reduce the amount of trash they generate and thus will help the parklands.

The fact that we can use landfills outside the county’s borders doesn’t impact the argument. (If the argument had been that we NEED TO reduce the amount of trash to save the parklands in the county, then this option would have weakened. Why? Because this option indicates that we don’t need to reduce the amount of trash to save the county’s parklands. We can simply use outside landfills. However, the current argument is not about what NEEDS to be done but about whether doing X will lead to Y.)