“Are you alone, my son?” asked a soft voice close behind me.

The correct answer is D. A soft voice behind me asked if I was alone.

The other options are incorrect because they do not accurately reflect the content of the question. Option A is incorrect because it does not specify that the voice was close behind the speaker. Option B is incorrect because it does not specify that the voice was soft. Option C is incorrect because it does not specify that the voice asked if the speaker was alone.

The question is asking if the speaker is alone. The answer is that a soft voice behind the speaker asked if they were alone. This is supported by the fact that the question states that the voice was close behind the speaker and that it was soft.