|Question 2Verbal

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Text
Researchers have long debated the origins of silver used in European coins from the 600s through the early 800s CE. Geochemical analysis by Kershaw et al. of 49 coins dating to 660–820 CE provides concrete evidence that reconciles two competing theories: early coins were made from Byzantine silver, and later coins used Frankish silver, findings that provide firm details in a previously ______ area of study.
Which choice completes the text with the most logical and precise word or phrase?
esoteric
A
authoritative
B
solitary
C
speculative
D