Complete the sentence: "Each of the suspects had (his or her, their) own alibi ready."

The sentence "Each of the suspects had (his or her, their) own alibi ready" is best completed with "his or her." This choice is grammatically correct because "each" is a singular pronoun, and it requires a singular possessive pronoun to maintain agreement in number.

Using "his or her" explicitly acknowledges that each suspect may be either male or female while maintaining singularity, which aligns with the concept of singular subjects being paired with singular pronouns. In formal writing, this is the preferred structure to ensure clarity and adherence to traditional grammatical rules.

While the choice "their" is often used informally in modern English as a gender-neutral plural pronoun, it does not align with the singular sense of "each suspect." This leads to potential grammatical ambiguity, which is typically advisable to avoid in formal contexts. The other options, such as "anyone's" and "her," are not applicable due to their lack of agreement with the singular subject.