Identify the erroneous segment; if none, choose ‘‘No error.’’ Sentence: His father told me that though his son had worked very hard, but he had failed to make any mark in the examination.

Introduction / Context:
This tests correct use of concessive conjunctions. In English, we do not pair ‘‘though/although’’ with ‘‘but’’; only one marker of contrast should be used.

Given Data / Assumptions:

• Concessive opener: ‘‘though’’ already appears in the sentence.
• Second contrast marker ‘‘but’’ appears later.

Concept / Approach:
Use either ‘‘though/although … , …’’ or ‘‘… , but …’’ but not both together. Retain the concessive clause and remove ‘‘but’’ to avoid redundancy.

Step-by-Step Solution:
Locate concessive pair: ‘‘though’’ + ‘‘but’’ → incorrect pairing.Delete ‘‘but’’ to make a clean concessive structure.Correct version: ‘‘… that though his son had worked very hard, he had failed to make any mark in the examination.’’

Verification / Alternative check:
Rephrase with ‘‘although’’ or switch to a simple ‘‘but’’ clause to see that a single contrast marker suffices.

Why Other Options Are Wrong:
A–C are grammatically fine and set up the concessive clause correctly; only D introduces the redundant ‘‘but.’’

Common Pitfalls:
Transferring structures from other languages where double marking may be idiomatic; overemphasizing contrast with two conjunctions.

Final Answer:
but he had failed to make any mark in the examination.