In the following passage, there are blanks, each of which has been denoted by a letter. For each blank, five options are given. Choose the most appropriate word from the options that fits the blank appropriately.

The development of agriculture stands as one of humanity's most ______ (A) historical achievements. Historians suggest early societies initially ______ (B) wild grains harvested from natural meadows or riverbanks. This opportunistic gathering eventually prompted the ______ (C) of systematic cultivation and irrigation methods.

Nomadic tribes gradually observed how seasonal rains ______ (D) crop yields, fueling both survival and permanent settlement. The transition from foraging to farming constituted a ______ (E) turning point in human civilization. Over generations, communities devised progressively refined tools to ______ (F) agricultural production, permanently altering the structure of society.

Which of the following words appropriately fits in blank (D)?

The correct answer is augmented.

Step-by-step explanation:
1. Analyze the Context:
The sentence states: "Nomadic tribes gradually observed how seasonal rains ______ (D) crop yields, fueling both survival and permanent settlement."
The phrase "fueling both survival and permanent settlement" clearly indicates that the effect of seasonal rains on crop yields was positive, beneficial, and productive.

2. Evaluate the Options:
• Impeded: Means hindered or obstructed, which carries a negative meaning and contradicts the positive impact mentioned.
• Depleted: Means diminished or exhausted, which is logically inconsistent with fueling survival.
• Curtailed: Means reduced or cut short, which would hinder settlement rather than support it.
• Restricted: Means limited or bound, which is negative in context.
• Augmented: Means increased, expanded, or enhanced. Seasonal rains increasing or enhancing crop yields perfectly fits the context of supporting human survival and permanent settlement.

3. Conclusion:
Therefore, the word augmented is the most appropriate fit for blank (D).