Choose the word that best replaces the words shown in bold in the sentence.…

Concept: A precise one-word substitution must preserve both a phrase’s core meaning and its contextual restriction. A noun that names the relevant kind of group is therefore preferable to a broader word that merely indicates several people together.

Application: The highlighted phrase describes an assembly identified by worship. “Congregation” has an established sense for people assembled as a religious community for worship, so it preserves both “assembly” and the religious context.

Contrast: The alternatives differ in the relationship they encode:

• “Crowd” identifies a large group in one place but does not encode why its members are together.

• “Gathering” identifies people meeting for any of many possible purposes, so its scope is broader.

• “Colleagues” identifies people connected by work or profession, which is a different relationship.

Cross-check: Substituting the word gives “The terrorists targeted the congregation on a holy day,” which remains grammatical and preserves the religious meaning of the original phrase.

Result: The best one-word replacement is “congregation”.