In 1980, Country A had a per capita gross domestic product (GDP) that was $5,000 higher than that of the European Economic Community. ██ █████ ███ ███████████ ████ ████████ ███ ██████████ ███ █████████ ██ ███████ █████ █ ██████ ███ ██████ ███ █████████ █ ██████ ███████ ████████ ██ ███████ ███ ███████ ████████ ██ ██████ ██ ███████ █ ████ ████ █████ ███████ ████ ███ █████
The argument concludes that between 1980 and 1990, Country A's average standard of living must have risen. This is supported by a claim that a rising per capita GDP indicates a rising standard of living—but how do we know that Country A's per capita GDP rose in that time?
This is the meat of the argument: the implicit sub-conclusion that Country A's per capita GDP rose between 1980 and 1990. This sub-conclusion is reached by comparing Country A's GDP with that of the European Economic Community in 1980 and in 1990. In 1980, Country A had a per capita GDP $5,000 higher than that of the EEC. By 1990, Country A was beating the EEC by $6,000.
The issue here is, just knowing the difference between these two polities doesn't tell us the absolute amount of Country A's per capita GDP at either time. Specifically, if the EEC's per capita GDP fell by more than $1,000, then Country A's per capita GDP wouldn't actually be higher in 1990 than in 1980, despite the higher difference with the EEC. So the argument must assume that the EEC's per capita GDP didn't fall more than $1,000 by 1990.
Which one of the following ██ ██ ██████████ ██ █████ ███ ████████ ████████
Between 1980 and █████ ███████ █ ███ ███ ████████ ████████ █████████ ███████████ ███ ████ ██████████ ████████ ██ ███████████
Per capita GDP is a product of two numbers: population, and overall gross domestic product. Either or both of these numbers can change to result in a different per capita GDP. So it's not necessary to assume a particular change in population for either Country A or the EEC.
Imagine Country A's population doubled, but its overall GDP more than doubled. That would result in an increased per capita GDP. Now imagine the EEC's population didn't change at all, and nor did its overall GDP, meaning no change in per capita GDP. That puts us in the same situation that the stimulus claims, where Country A's per capita GDP increased—even though the percentage change in population between Country A and the EEC was different.
Between 1980 and █████ ███ ███████ ████████ ██ ██████ ██ ███ ████████ ████████ █████████ █████
Average standard of living increases as per capita GDP increases—so to establish that Country A's standard of living increased, the argument needs to show that its per capita GDP increased. (B) actually weakens that reasoning: if the EEC's per capita GDP decreased, then Country A's per capita GDP may also have decreased, even though it gained more of an advantage over the EEC.
Some member countries ██ ███ ████████ ████████ █████████ ████ ██████ ███ ██████ █ ██████ ███████ ████████ ██ ██████ ████ ███████ ██
Because the argument compares Country A against the EEC as a whole, divergences within the individual member countries of the EEC aren't relevant to the argument, making them unnecessary to assume. The argument also isn't concerned with Country A's standard of living as compared with that in the EEC; the EEC is just used to demonstrate an increase in Country A's standard of living.
The per capita ███ ██ ███ ████████ ████████ █████████ ███ ███ █████ ██ ████ ████ ██████ ██ ████ ████ ██ ███ ████ ██ █████
The argument only tells us the difference between Country A's per capita GDP and that of the EEC in 1980 and in 1990. We don't learn the actual numbers. So even though the difference increased by $1,000 by 1990, if the EEC's per capita GDP number fell by more than $1,000, that would cancel out the change in the difference, leaving Country A with no increase and the argument broken apart.
Because the argument can't function without (D) being true, we can tell that (D) is necessary to assume. (D) must be true for the argument to make any sense.
In 1990, no ██████ ███████ ██ ███ ████████ ████████ █████████ ███ █ ███ ██████ ███ ██████ ████ ████ ██ ███████ ██
(E) has the same problem as (C): the argument compares Country A with the EEC as a whole, so it's not necessary to assume anything about individual members of the EEC. All we need to assume about the EEC is that its per capita GDP didn't fall by more than $1,000.
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