Spot an error in the given sentence. (A) Every girl and boy in a class / (B)…

Concept: Subject–verb agreement is governed by the grammatical number of the subject, not merely by the conjunctions joining its parts. Distributive determiners — ‘each’, ‘every’, ‘either’, ‘neither’ — placed before a subject made of two or more nouns joined by ‘and’ force the whole subject to be treated as singular, because each item is considered individually rather than jointly. Such subjects therefore always take a singular verb.

Application: Applying this rule to the given sentence step by step:

1. Identify the subject of the sentence: ‘Every girl and boy in a class’.

2. Note the determiner ‘Every’ governing the compound noun ‘girl and boy’ — this makes the subject singular in sense, even though two nouns are joined by ‘and’.

3. Check the verb used with this subject: ‘have written’ — ‘have’ is the plural present-tense auxiliary.

4. Since the subject is singular (because of ‘every’), the correct auxiliary is the singular form ‘has’, giving ‘has written’.

5. This mismatched verb occurs in part (B) of the sentence, so (B) is the part containing the error.

Cross-check: Substituting the corrected verb confirms the rule — ‘Every girl and boy in a class has written a letter to the Principal of the school to grant scholarship’ reads correctly. The same pattern holds elsewhere, e.g. ‘Every teacher and student is invited’ (not ‘are invited’). Parts (A) and (C) contain no comparable agreement or structural issues, which rules out ‘No error’ (D) as well.

Result: The error lies in part (B); ‘have’ must be replaced by ‘has’.