Let's break this one down:

Aroca City currently funds its public schools through taxes on property.
Fact ---> property tax pays for schools

In place of this system, the city plans to introduce a sales tax of three percent on all retail sales in the city.
Proposal ---> they plan to change from property taxes to sales tax

Critics protest that three percent of current retail sales falls short of the amount raised for schools by property taxes.
Objection -----> retail sales tax < property tax (thus, plan is bad)

The critics are correct on this point.
Concession ---> yes, but...

Nevertheless, implementing the plan will probably not reduce the money going to Aroca's schools.
Rebuttal---> retail sales tax actually not less than property tax

Several large retailers have selected Aroca City as the site for huge new stores, and these are certain to draw large numbers of shoppers from neighboring municipalities, where sales are taxed at rates of six percent and more.
Explanation ---> new shopping center will be built ===> more tax revenue

In consequence, retail sales in Aroca City are bound to increase substantially.
Support ---> more sales = more tax revenue


On to the question...

In the argument given, the two potions in boldface play which of the following roles?

(A) The first is an objection that has been raised against a certain plan; the second is a prediction that, if accurate, undermines the force of that objection.
Yes, this is it. If there are more sales from the shopping center, then the sales tax revenue could potentially be greater than or equal the property taxes, which is the objection to the plan in question.

(B) The first is a criticism, endorsed by the argument, of a funding plan; the second is a point the argument makes in favor of adopting an alternative plan.
The first part is correct, but the second part is wrong. An alternative plan is never mentioned in the passage.

(C) The first is a criticism, endorsed by the argument, of a funding plan; the second is the main reason cited by the argument for its endorsement of the criticism.
Again, first half of the sentence is correct, but the second part is incorrect. The second sentence in bold supports the rebuttal to the objection to the plan proposed by the city.

(D) The first is a claim that the argument seeks to refute; the second is the main point used by the argument to show that the claim is false.
Yes on the first part, no on the second. Nothing is proven false as everything is still hypothetical. The shopping center has yet to be built.

(E) The first is a claim that the argument accepts with certain reservations; the second presents that claim in a rewording that is not subject to those reservations.
Trap answer. Everything is good up until the word “rewording.” There is no rewording done in the passage.

Answer Choice A