SAT Question 0afb2ac4: Words In Context answer and explanation

English - Words In Context - Fill In Blank Single Word
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Ancient Inca inhabiting the Andes Mountains used terraces, rows of flattened land with built-in irrigation systems, to grow crops at different altitudes. This method of farming proved to be highly ______, as evidenced by the great number and variety of crops grown at that time.
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Difficulty:Easy
Which choice completes the text with the most logical and precise word or phrase?