单选题 A Principal known for B his C dictionary , Noah Webster was also the first D epidemiologist in the country.

【正确答案】 A

【答案解析】解析：Principal一Principally。句意：大部分人知道诺亚·韦伯斯特是因为他的字典，可他还是国内第一个流行病学家。principal为形容词，而修饰动词known应用副词，故答案为A。