Select the correct indirect form of the given sentence.

"If you don't keep quiet I shall shoot you", he said to her in a calm voice. 

He warned her calmly that he would shoot her if she didn’t keep quiet.

The correct indirect form of the given sentence is:

He warned her calmly that he would shoot her if she didn't keep quiet.

The other options are incorrect for the following reasons:

• He warns her calmly that he will shoot her if she didn’t keep quiet. - The present tense verb "warns" is not appropriate in indirect speech, as the speaker is reporting what was said in the past.
• He warn her calmly that he will be shooting her if she didn’t keep quiet. - The future tense verb "will be shooting" is not appropriate in indirect speech, as the speaker is reporting what was said in the past.
• He warned her calmly that he would shoot her if she do not remain silent. - The phrase "do not remain silent" is not as natural-sounding as the phrase "didn't keep quiet".