The treaty specifies that the economy of the member nations have infla

The answer is B.

A can be eliminated because "economy of the member nations" suggests that all the nations together have one economy.

C is awkward in putting "every" before "economy" instead of "nation." It is not clear from C that each member nation has one economy.

D and E can be eliminated because "economies of each member nation" and "economies of every member nation" imply that each member nation has more than one economy.

In B, the verbs "have" and "be" are correct because "treaty specifies that" is an expression of requirement, which takes the subjunctive: "The treaty specifies (i.e. requires) that the economy of each member nation have... and be..."
The present subjunctive is required in that clauses after verbs of requirement, recommendation, and request. These verbs include: require, mandate, insist, command, demand, stipulate, recommend, propose, suggest, urge, advise, move, request, ask, desire. The present subjunctive is also used in that clauses after adjectives and nouns derived from these verbs: required, requirement, requested, request, desirable, recommended, recommendation, proposed, proposal, suggested, suggestion, advised, advisable, advice, motion, etc. It is also used in that clauses after other adjectives and nouns of requirement, recommendation, and request: necessary, essential, critical, vital, imperative, urgent, important, condition.



Here are some real GMAT Sentence Correction sentences that use the present subjunctive:



The Gorton-Dodd bill requires that a bank disclose to its customers how long it will delay access to funds from deposited checks.



Legislation in the Canadian province of Ontario requires of both public and private employers that pay be the same for jobs historically held by women as for jobs requiring comparable skill that are usually held by men.



In one of the most stunning reversals in the history of marketing, the Coca-Cola company in July 1985 yielded to thousands of irate consumers who demanded that it bring back the original Coke formula.



The commission proposed that funding for the development of the park, which could be open to the public early next year, be obtained through a local bond issue.



Most state constitutions now mandate that the state budget be balanced each year.



Despite protests from some waste-disposal companies, state health officials have ordered that the levels of bacteria in seawater at popular beaches be measured and the results published.



Judicial rules in many states require that the identities of all prosecution witnesses be made known to defendants so that they can attempt to rebut the testimony, but the Constitution explicitly requires only that the defendant have the opportunity to confront an accuser in court.



During her presidency of the short-lived Woman’s State Temperance Society (1852-1853), Elizabeth Cady Stanton, a staunch advocate of liberalized divorce laws, scandalized many of her most ardent supporters by suggesting that drunkenness be made sufficient cause for divorce.



Several financial officers of the company spoke on condition that they not be named in the press reports.



The new regulations mandate that a company allow its retiring employees who would otherwise lose group health care coverage to continue the same insurance at their own expense for a specific period.



Bankers require that the financial information presented to them by mortgage applicants be complete and follow a prescribed format.

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