Twenty years ago the Republic of Rosinia produced nearly 100 million tons of potatoes, but last year the harvest barely reached 60 million tons. Agricultural researchers, who have failed to develop new higher-yielding strains of potatoes, are to blame for this decrease, since they have been concerned only with their own research and not with the needs of Rosinia. Which one of the following is an assumption on which the argument depends? ['Agricultural researchers often find concrete solutions to practical problems when investigating seemingly unrelated questions.', 'Strains of potatoes most commonly grown in Rosinia could not have produced the yields last year that they once did.', 'Agricultural research in Rosinia is funded by government grants.', 'Wide fluctuations in the size of the potato crop over a twenty-year period are not unusual.']