Answer:
Colloquial expressions
Ambiguous pronoun usage
Explanation:
Colloquial expressions should be avoided because a paper is a formal document, and colloquial expressions are typical of informal language. Besides, many colloquial expressions are very local in nature and do not translate well for either native english speakers from other areas, or for people who have english as a second language.
Ambiguous pronoun usage should be avoided because as the adjective implies, it leads to ambigious, confusing meanings, and the goal of an academic paper should be to express ideas with as much clarity as possible.
