In the following English grammar error detection question, identify the part of the sentence that contains an error, or choose "No error" if the sentence is correct: I have learned that what really counts in life, in the end, is not how many toys we have collected or how much money we have accumulated, but how many of our talents we have liberated and used for a purpose that add value to this world.

Introduction / Context:
This error detection question tests your understanding of subject verb agreement and how relative clauses work inside a long, complex sentence. The sentence talks about what really matters in life and then narrows down to a phrase about a purpose that adds value to the world. The goal is to see whether you can track the true subject and match it with the correct verb form.

Given Data / Assumptions:

• The sentence is divided into four numbered parts, with the fourth part representing "No error".
• The line containing "a purpose that add value to this world" is labelled part 3.
• The overall sentence structure and ideas should be kept as they are; only grammar and usage are being checked.
• The main focus is likely on agreement or tense consistency rather than vocabulary.

Concept / Approach:
Subject verb agreement means that a singular subject must take a singular verb and a plural subject must take a plural verb. In relative clauses starting with "that", the verb inside the clause must agree with the noun that "that" refers to. In the phrase "a purpose that add value", the noun "purpose" is singular. Therefore, the verb that follows the relative pronoun "that" must also be singular: "adds", not "add". Everything else in the sentence is grammatically acceptable and idiomatic.

Step-by-Step Solution:
Locate the relative clause: "that add value to this world".Identify the antecedent of "that". It refers back to "a purpose", which is singular.Apply subject verb agreement. A singular subject ("purpose") requires the singular verb "adds".Notice that the sentence currently uses the plural verb "add", which does not match the singular subject.Conclude that the error is in the part containing "a purpose that add value to this world", that is, part 3.

Verification / Alternative check:
If we correct the sentence to "a purpose that adds value to this world", the clause now reads smoothly. The rest of the sentence "I have learned that what really counts in life, in the end, is not how many toys we have collected or how much money we have accumulated, but how many of our talents we have liberated and used for a purpose that adds value to this world" is grammatically sound and stylistically natural.

Why Other Options Are Wrong:
Part 1 correctly uses the present perfect "have learned" and has proper commas. Part 2 is fine in terms of structure and agreement when it speaks of toys and money. Part 4 is simply the "No error" choice and cannot be selected if any real error exists in parts 1 to 3. Since the only clear error is the mismatch between "purpose" and "add", part 3 must be chosen.

Common Pitfalls:
Many learners are distracted by the length of the sentence and the emotional vocabulary about life, talents, and value. Because there are many plural nouns like "toys", "talents", and "we", students may overlook the singular noun "purpose" near the end and accept "add" without checking. A useful exam strategy is to examine each chunk separately and always check agreement in relative clauses that use "who", "which", or "that".

Final Answer:
The error is in part 3, where "a purpose that add value to this world" should read "a purpose that adds value to this world".