Select the option that will improve the highlighted part of the given sentence. In case no improvement is needed, select 'No improvement required'.
I am sorry of which my mother said.

Correct option is A

The correct substitution of the highlighted phrase is "for what".
· The phrase "of which" is incorrect in this sentence.
· The correct phrase "for what" means "regarding the thing that", which fits the context properly.
Example:
· Incorrect: I am sorry of which my mother said.
· Correct: I am sorry for what my mother said.
Grammatical Rule Used:
· "For what" is used when referring to something that has been said or done.
Meanings of other options:
· (b) for which – Incorrect, as "which" requires an antecedent.
· (c) off that – Incorrect, "off" does not fit grammatically.
· (d) No improvement required – Incorrect, as the phrase is grammatically wrong.