English grammar error-spotting (idiom and collocation: choose the single erroneous part among A–D; select ‘‘No error’’ only if the sentence is fully correct): ‘‘He explained the matter / at great length / but I was not the wiser / No error.’’

Given data

• A: ‘‘He explained the matter’’
• B: ‘‘at great length’’
• C: ‘‘but I was not the wiser’’
• D: ‘‘No error.’’

Concept / Approach
Identify the fixed idioms. ‘‘At great length’’ is a correct collocation meaning ‘‘very thoroughly/for a long time’’. The idiomatic result phrase is ‘‘none the wiser’’, not ‘‘not the wiser’’.

Step-by-step analysis
Check B → valid idiom ‘‘at great length’’.Check C → replace with the fixed idiom ‘‘none the wiser’’.

Correction
‘‘He explained the matter at great length, but I was none the wiser.’’

Common pitfalls

• Substituting ‘‘not’’ for the fossilized phrase ‘‘none the’’ in this idiom.

Final Answer
but I was not the wiser