Understanding the argument -
In theory, Papua New Guinea could be a substantial exporter of tropical crops. - Opinion + Premise
In actuality, it is not. - Fact
The reason is that 97 percent of all land is owned by clans and cannot be bought or sold by individuals, and thus the kinds of realignment of properties that would be necessary to achieve maximum production for export have been impossible to achieve. - Supporting premise + Conclusion
Option Elimination - Evaluating the adequacy of the explanation given above.
(A) Who owns the 3 percent of the land in Papua New Guinea that is not owned by clans? - How does it even matter who owns it? Out of scope.
(B) What percentage of Papua New Guinea’s current production of tropical crops is consumed within the country? - Say it's 1% or 99%. But how does that relate to the scope of the argument, which is the "issue of whether property realignment is the primary hindrance to exporting tropical crops from Papua New Guinea." Out of scope.
(C) How much longer is land ownership by clans expected to remain the prevailing cultural pattern in Papua New Guinea? - Out of scope.
(D) Which of the tropical crops currently grown in Papua New Guinea could be exported if there were a surplus for export? - Out of scope.
(E) How does Papua New Guinea’s current production capacity for tropical crops compare with the maximum capacity that property realignment would make possible? Ok.
Say, it's close - then the validity of the reason is weakened. Then "property realignment is not the primary hindrance to exporting tropical crops from Papua New Guinea"
Say there is a major gap, then this reasoning is strengthened.