Grammar
Grammar questions are agreement questions
Most grammar items in business writing test three things: agreement, case, and consistency of tense.
Subject–verb agreement. Find the true subject and ignore interrupting phrases: The box of invoices is on the desk. Indefinite pronouns - each, either, everyone, nobody, one - are singular: Each of the managers has filed a report. With either/or and neither/nor, the verb agrees with the nearer subject: Neither the supervisor nor the employees were notified. Collective nouns (team, committee, staff) take a singular verb when they act as one unit.
Pronoun agreement and case. A pronoun must match its antecedent in number: Every applicant must submit his or her résumé, or rewrite in the plural: Applicants must submit their résumés. Case depends on function: subject pronouns (I, he, she, they) perform the action, object pronouns (me, him, her, them) receive it or follow a preposition. Between you and me; for whom; who called? Quick test: substitute he or him - if him fits, use whom.
Tense consistency. Keep one tense across a paragraph unless the timeline genuinely shifts. She reviewed the file and noticed the error, not notices.
Verb forms. Business writing traps had went (had gone), have wrote (have written), should of (should have), and comparisons left unfinished (better needs a than).
Rule of thumb: strip the sentence down to subject and verb before deciding anything. Most agreement errors vanish once the modifiers are taken out of the way.