In this error-spotting sentence, identify the part that contains an error in subject–verb agreement or plural formation: "My sister-in-laws who lives in Kolkata have come to stay with us."

Introduction / Context:
This question focuses on correct plural formation of compound nouns and agreement between subject and verb. The phrase sister in law is a compound noun, and it has a special pattern for pluralisation. Many learners make mistakes with such forms, especially when they are part of longer sentences involving relative clauses like who lives in Kolkata. Error spotting in such contexts is common in competitive exams.

Given Data / Assumptions:

• Part 1: My sister-in-laws
• Part 2: who lives in Kolkata
• Part 3: have come to stay with us.
• Part 4: No Error
• We assume there is more than one sister in law visiting.

Concept / Approach:
For compound nouns like sister in law, the plural is formed by adding s to the main noun, not to law. Therefore, the correct plural is sisters in law, not sister in laws. Once we fix that, agreement of who lives and have come also needs attention, but the primary test in this question is the plural form in part 1. Standard exam keys usually treat one main error per sentence, and the clearly visible error is the wrong pluralisation of sister in law.

Step-by-Step Solution:
Step 1: Identify the head noun in the compound sister in law, which is sister. Step 2: Apply the rule that the plural marker s is attached to sister, producing sisters in law. Step 3: Notice that the given phrase My sister-in-laws contradicts this rule. Step 4: Recognise that therefore part 1 contains a clear and important grammatical error. Step 5: Select option 1 as the part with error.

Verification / Alternative check:
Rewrite the sentence correctly as My sisters-in-law who live in Kolkata have come to stay with us. Here, both the plural form and the verb agreements are corrected. Since the exam typically counts only one part as erroneous in such a pattern, part 1, containing sister-in-laws, is clearly wrong. Even if you notice that lives should be live, the most obvious and tested concept here is compound noun pluralisation in part 1.

Why Other Options Are Wrong:
Part 2 contains who lives in Kolkata, and while live would be better if we emphasise more than one person, the highlighted central test point is the plural compound noun.

Part 3, have come to stay with us, correctly uses have as an auxiliary for a plural subject, matching sisters in law once corrected.

Part 4, No Error, cannot be chosen because we have already identified the incorrect plural form in part 1.

Common Pitfalls:
Students often add s at the very end of a compound noun, especially in speech, without considering which word carries the main meaning. This leads to forms like brother in laws or mother in laws. Remember that in such compounds, the first noun generally takes the plural, leading to brothers in law, mothers in law, and sisters in law.

Final Answer:
The error is in part 1; the correct form should be My sisters-in-law.