Error Spotting – Choose the segment (A–D) that contains a grammatical error; select “No error” only if the entire sentence is correct. Sentence: A) Each cigarette B) a person smoke C) does some harm and eventually D) it may cause a serious disease.

Introduction / Context:
This tests subject-verb agreement in a relative-like clause without an explicit relative pronoun. After “Each cigarette”, the embedded clause describing what a person does must use a third-person singular verb form with “a person”.

Given Data / Assumptions:

• Head determiner: “Each” → singular notion.
• Embedded subject: “a person”.
• Verb form used: bare “smoke” instead of “smokes”.

Concept / Approach:
With “a person/he/she”, the present simple verb takes the -s inflection. Therefore, the natural reading is “Each cigarette a person smokes …”.

Step-by-Step Solution:
1) Locate the subject of the embedded clause: “a person”.2) Apply 3rd-person singular agreement: “smokes”.3) Correct sentence: “Each cigarette a person smokes does some harm, and eventually it may cause a serious disease.”4) Hence the error is in B.

Verification / Alternative check:
Substitute pronoun: “Each cigarette he smokes …” confirms the -s requirement.

Why Other Options Are Wrong:

• A: “Each cigarette” correctly sets up singular reference.
• C–D: Idiomatic and semantically coherent.

Common Pitfalls:
Dropping the -s after “each … a person …” frames; treating “person” as plural.

Final Answer:
Option B