In the following sentence, identify the part that contains a grammatical error, or choose No error if the sentence is correct: Mother does not hardly know what happened in school yesterday.

Introduction / Context:
This question belongs to the error spotting category in English grammar, a very frequent type in competitive exams. The task is to examine each part of the sentence and locate the portion that contains a grammatical mistake. The sentence talks about a mother and her knowledge of what happened in school yesterday. The error relates to the use of negatives and adverbs, specifically a double negative construction that is not acceptable in standard English.

Given Data / Assumptions:

• Complete sentence: Mother does not hardly know what happened in school yesterday.
• Part A: Mother does not hardly.
• Part B: know what happened.
• Part C: in school yesterday.
• Part D: No error.
• We must identify the part that has a grammatical problem.

Concept / Approach:
In standard English, using two negatives to express a single negative idea is considered incorrect in formal writing. The phrase does not hardly creates a double negative effect, because not is a negative auxiliary and hardly is a negative adverb meaning scarcely. The correct expression should be either hardly knows or does not really know, but not does not hardly know. Therefore, the error lies in Part A, where the combination of not and hardly is grammatically faulty.

Step-by-Step Solution:
Step 1: Read the full sentence to understand its meaning: the mother scarcely knows what happened. Step 2: Focus on Part A: Mother does not hardly. Here not and hardly both contribute negative force. Step 3: Recognise that standard modern English avoids double negatives; the sentence should use either does not know much or hardly knows. Step 4: Check Part B: know what happened, which is grammatically fine and clearly expresses what she knows. Step 5: Check Part C: in school yesterday, which correctly indicates place and time.

Verification / Alternative check:
Try correcting the sentence. Possible correct versions include Mother hardly knows what happened in school yesterday or Mother does not really know what happened in school yesterday. In both cases, only one negative idea is used. Compare this with Mother does not hardly know, which would literally suggest she does hardly know, creating confusion. Because only Part A must be changed to remove the double negative, it is clear that Part A contains the error and is therefore the correct answer for the error location.

Why Other Options Are Wrong:

• know what happened: This phrase is grammatically correct and logically connected to the subject and verb.
• in school yesterday: Correctly expresses the place and time adverbial and does not contain any error.
• No error: This would be chosen only if there were no grammatical mistakes in the sentence, but the double negative in Part A proves otherwise.

Common Pitfalls:
Students sometimes miss double negatives because in informal speech people use them for emphasis. Phrases like cannot hardly or do not never may occur in casual language, but they are not acceptable in formal examination English. Another pitfall is focusing only on verb forms and ignoring adverbs like hardly, scarcely or barely, which already carry a negative sense. When spotting errors, pay special attention to combinations of auxiliaries and negative adverbs to avoid missing such issues.

Final Answer:
The erroneous part is Mother does not hardly, that is, option A, because it creates an incorrect double negative construction in standard English.