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The following indefinite pronouns may be either singular or plural, depending on the sense of the sentence.
all any most none some
If the pronoun refers to one person or thing, it is singular and takes a singular verb. If the pronoun refers to more than one person or thing, it is plural and requires a plural verb.
Some of the excitement of being on vacation was lost after the first three days. (Some refers to excitement, which is singular.)
Some of the students prefer Sarah for class president; others prefer Andy. (Some refers to students, which is plural.)
To indicate whether they are singular or plural, the subjects of the two preceding sentences can be diagramed as shown below.