When uncontrollable factors such as lack of rain cause farmers’ wheat crops to fail, fertilizer and seed dealers, as well as truckers and mechanics, lose business, and fuel suppliers are unable to sell enough diesel fuel to make a profit.
Statements
On Must Be True we primarily read for wording clues of a Conditional, Causal, or Quantitative variety.
This paragraph has a Conditional "when", which is a sufficient indicator (put it on the left of the arrow).
And there is definitely causal language, such as "causes" and the implied repercussions of that first effect.
We can kind of combine our Conditional and Causal thinking then, and just articulate to ourselves the chain of causality.
1. Some uncontrollable factor such as a lack of rain causes wheat crops to fail.
2. The seed and fertilizer industry gets hurt.
3. Truckers and mechanics get hurt.
4. Fuel suppliers struggle.
The paragraph essentially describes an ecosystem of the economy that is intertwined with the wheat farmers.
Goal
It's hard to make a specific guess here, but one would think it would reinforce connecting that first cause from the final effect (or some subset of the causal chain).
Since a lack of rain could lead to fuel suppliers being unable to make a profit, you can say something like .
We don't know what to expect, but we'll be on guard for stuff that's Too Strong, Out of Scope, or Illegal Logic (reversals / opposites).