Twenty years ago the Republic of Rosinia produced nearly 100 million tons of potatoes, but last year the harvest barely reached 60 million tons.
Conclusion
Agricultural researchers are to blame for this decrease (potato harvest).
Evidence (since)
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 failed to develop new higher-yielding strains of potatoes.
They (agricultural researchers) have been concerned only with their own research and not with the needs of Rosinia.
Evaluate
When we see change over time on the LSAT, chances are high that we're going to be tested on the idea of the causal difference maker: what caused that change over time. Typically, the conclusion will posit one causal difference maker, and it's our job to assess how plausible that is. In this argument, the change is a dramatic decrease in the potato harvest over the period of 20 years. The conclusion posits that Ag researchers are to blame for not developing higher-yielding strains. But why would we need new, higher-yielding strains if we already had strains that could produce 100 million tons back in the day?
Goal
Look for an answer that rules out an alternative causal difference maker, or an answer that defends against our objection that we already have strains that should be sufficient to produce the big yields of years past. Since Necessary Assumption questions aren't always that predictable, read each answer with an open mind and beware answers that are too strong.