Select the most appropriate direct form of the given sentence.
His mother told him to phone his father at once.

Correct option is A

The correct direct speech is option (a).
Rule Explanation:
Imperative sentences (giving orders or instructions) in indirect speech use the structure:
• told + to + base verb
In direct speech, we return it to the imperative: “Base verb + object”
Pronoun “his” becomes “your” when addressing directly.
Structure:
Indirect: told him to + base verb
Direct: said to him, “base verb + object + time phrase”
Example:
Indirect: She told me to close the door.
Direct: She said to me, “Close the door.”
In imperative sentences, modal verbs like must/should change the tone. “Told him to” simply becomes a command in direct.