Replace `had attained’ by `attained’.

The given sentence contains an error in Part 3 where the word "attained" has been used instead of "achieved". "Attained" means to reach or come to, while "achieved" means to successfully accomplish a goal or task. In the context of India's independence, it is more appropriate to use the word "achieved" as it denotes the successful struggle and efforts put in by Indian freedom fighters to attain independence.

The corrected sentence should read as follows:

The teacher told the students - This part of the sentence is grammatically correct and does not contain any error.

that - This is a conjunction used to introduce a subordinate clause in the sentence and is also grammatically correct.

India had achieved independence - The correct word to be used here is "achieved" instead of "attained". This part of the sentence contains the error.

on 15th August 1947 - This part of the sentence is grammatically correct and provides the specific date of India's independence.

No Error - This option is not the correct answer as there is an error in the given sentence.

Therefore, option C, i.e. Part 3, is the correct answer.

Formulae:

Attain: To reach or come to something, especially after a lot of effort.

Achieve: To successfully accomplish a goal or task.

Key takeaways:

The given sentence contains an error in Part 3 where the word "attained" has been used instead of "achieved".

In the context of India's independence, it is more appropriate to use the word "achieved" as it denotes the successful struggle and efforts put in by Indian freedom fighters to attain independence.

The corrected sentence should read as follows: "The teacher told the students that India had achieved independence on 15th August 1947."

Option C, i.e. Part 3, is the correct answer.