In this error spotting question, the sentence is divided into parts labelled (A), (B), (C), and (D). Identify the part that contains an error: "My younger sister (A) / is much smarter (B) / then me. (C) / No error (D)".

Introduction / Context:
Error spotting questions are designed to test your command of basic grammar and usage. Here, the sentence "My younger sister is much smarter then me." has been divided into four labelled parts. You must identify which part contains a grammatical error. The focus in this sentence is on the correct use of "than" and "then" in comparative constructions.

Given Data / Assumptions:

• Part A: "My younger sister"
• Part B: "is much smarter"
• Part C: "then me."
• Part D: "No error"
• The intended meaning is a comparison of intelligence between the speaker and his or her younger sister.

Concept / Approach:
In English, "than" is a conjunction used in comparisons, as in "taller than me" or "smarter than you". "Then" refers to time or sequence, as in "first we went to the market, then we went home". Because the sentence is clearly a comparison (smarter than someone), the correct word is "than", not "then". Therefore the error lies in the part where "then me" appears. The rest of the sentence is grammatically fine in everyday English, even though in very formal writing some would prefer "smarter than I am". For exam purposes, correcting "then" to "than" is the key point.

Step-by-Step Solution:
Step 1: Read the full sentence: "My younger sister is much smarter then me." Step 2: Identify that the structure "smarter ... me" is a comparative construction. Step 3: Recall that comparisons require "than", not "then". Step 4: Check Part A: "My younger sister". This is a grammatically correct noun phrase. Step 5: Check Part B: "is much smarter". This is a correct comparative predicate. Step 6: Check Part C: "then me." Here, "then" is incorrectly used in place of "than". Step 7: Conclude that Part C is the only part containing an error.

Verification / Alternative check:
Rewrite the sentence in correct form: "My younger sister is much smarter than me." You can also make it slightly more formal: "My younger sister is much smarter than I am." In both versions, "than" is the correct word. Replacing "then" with "than" removes the error, while all other parts remain unchanged. This confirms that the mistake is restricted to Part C.

Why Other Options Are Wrong:
Part A correctly introduces the subject. Part B correctly uses the verb "is" and the comparative adjective "smarter" with the modifier "much". Part D saying "No error" is wrong because we have clearly identified an error in Part C. There is no second grammatical error in the sentence that would justify choosing "More than one part has an error".

Common Pitfalls:
A common weakness for learners is confusion between "than" and "then" because they sound similar. Many people also worry unnecessarily about whether to say "than me" or "than I". While very formal grammar prefers "than I", modern standard English widely accepts "than me", especially in spoken language. Exam questions at this level typically focus on the obvious misuse of "then" in a comparative context, not on the subtle stylistic choice between "than me" and "than I".

Final Answer:
The error is in Part C: then me., where "then" should be replaced by "than".