Question

look at this thesaurus entry:
critical
part of speech: adjective
definition: negative
synonyms: against, opposing, unfavorable
which might be described as critical?
a customer who complains
a number that is less than zero

Explanation:

To determine which can be described as "critical", we use the thesaurus entry. "Critical" (as an adjective with a negative - related definition and synonyms like against, opposing, unfavorable) fits a customer who complains (since complaining is a negative, opposing action). A number less than zero is a "negative number" in a mathematical sense, but the thesaurus defines "critical" as negative in a non - mathematical, evaluative sense. So a customer who complains is critical.

Answer:

a customer who complains