input: Text: THE MOONS OF MARS By DEAN EVANS Illustrated by WILLER Every boy should be able to whistle, except, of course, Martians. But this one did! He seemed a very little boy to be carrying so large a butterfly net. He swung it in his chubby right fist as he walked, and at first glance you couldn't be sure if he were carrying it, or it carrying him. He came whistling. All little boys whistle. To little boys, whistling is as natural as breathing. However, there was something peculiar about this particular little boy's whistling. Or, rather, there were two things peculiar, but each was related to the other. The first was that he was a Martian little boy. You could be very sure of that, for Earth little boys have earlobes while Martian little boys do not—and he most certainly didn't. The second was the tune he whistled—a somehow familiar tune, but one which I should have thought not very appealing to a little boy. "Hi, there," I said when he came near enough. "What's that you're whistling?" He stopped whistling and he stopped walking, both at the same time, as though he had pulled a switch or turned a tap that shut them off. Then he lifted his little head and stared up into my eyes. "'The Calm'," he said in a sober, little-boy voice. "The what?" I asked. "From the William Tell Overture," he explained, still looking up at me. He said it deadpan, and his wide brown eyes never once batted. "Oh," I said. "And where did you learn that?" "My mother taught me." I blinked at him. He didn't blink back. His round little face still held no expression, but if it had, I knew it would have
  Question: How does the narrator know that the little boy and his mother are with the Martians at the fire?
  
   (A) He hears the boy whistling. 
   (B) He follows them there. 
   (C) Wahanhk tells him where to find them. 
   (D) They live there. 
  Answer:
output: He hears the boy whistling.