Select the correct indirect form of the given sentence.
I said to the postman, “Is there a letter for me?”

Correct option is C

The correct indirect form of the given sentence is (c) I asked the postman if there was a letter for me.
Direct speech- Direct speech, also known as quoted speech or direct quotation, is a way of reporting someone's exact words.
Indirect speech- Indirect speech, also known as reported speech or indirect quotation, is a way of reporting someone's words or thoughts indirectly, without using their exact words.
Rules for changing direct speech to indirect speech for interrogative sentence-
· When the reporting verb of direct speech is in past tense then all the present tenses are changed to the corresponding past tense, past indefinite changes to past perfect and past continuous changes to past perfect continuous in indirect speech. 
· No conjunction is used, if a sentence in direct speech begins with a question (what/where/when) as the “question-word” itself acts as a joining clause.
· If a direct speech sentence begins with an auxiliary verb/helping verb, the joining clause should be  if or whether.
· Reporting verbs such as ‘said/ said to’ changes to enquired, asked, or demanded.