Select the option that expresses the given sentence in indirect speech.
“We must be vigilant. Our teacher never accepts the assignment if any one of us is late in submission,” Ramesh said to his friend.

Correct option is B

The correct expression in indirect speech is (b) "Ramesh told his friend that they must be vigilant as their teacher never accepted the assignment if any one of them was late in submission."
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 converting direct speech to indirect speech-
· When the reporting verb of direct speech is in past tense then all the present tenses are changed to the corresponding past tense in indirect speech. 
· Reporting verbs such as ‘said/ said to’ changes to said, told.
· Comma inverted comma will be replaced with conjunction “That”.
· The  first person in direct speech  changes as per the subject of the speech.
· The  second person of direct speech  changes as per the object of reporting speech.
· The  third person of direct speech  doesn’t change.
This option correctly changes the direct speech into reported speech, adjusting the pronouns and verb tenses to reflect the shift from direct dialogue to a reported statement. The use of "told" is appropriate for reporting advice or warnings.