He knows so much about Russia that he's universally acknowledged as a(n) on Russian affairs.
A. authority
B. routine
C. privilege
D. boundary
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(答案→)A. authority
B. routine
C. privilege
D. boundary
解析：考查名词：A. authority官方，权威B. routine常规C. privilege特权D. boundary边界，句意：他对俄罗斯是如此了解以至于被公认为是俄罗斯问题的权威。选A。