I don’t understand what your asking?
This is because in the "U.S.A.", people in all the regions in the U.S.A. historically migrated throughout an "entire land mass" (essentially) ; and this "land mass" tends to be more "homogeneous" (as opposed to "British English" speakers; who speak with different dialects, accents). Note that the United Kingdom, including Great Britain, is further isolated from the U.S.A.—by a huge ocean— than the "relatively more homogeneous physical region"/ and thus the "relatively more linguistic region".
Answer:
a
Explanation:
There are three (3) main articles used in English language and these are;
1. An: it is a word that is mainly used before words beginning with any of the vowel letters (a, e, i, o and u). It's an indefinite article used for modifying non-specific (unspecific) nouns.
2. A: it is mainly used with consonant sounds or letters. It's an indefinite article used for modifying non-specific (unspecific) nouns.
3. The: it is a definite article used before nouns or superlative adjectives to indicate uniqueness.
In this scenario, the most appropriate article to use is "a" because it describes the position held by Thapa.
Mr. Thapa is a university professor.