Concept:The mosquito pupa lives in water but breathes air from the surface through a pair of tube-like breathing organs on its back (thorax).Explanation:The pupa ("tumbler") rests just under the water surface with its two breathing tubes touching the air.Air passes through these tubes into its body.Among the options, these tubes are the siphons. The pupa has no lungs and no gills, and the trachea is the internal air tube system, not the surface breathing tube.Key point: The larva breathes through a single siphon at its tail end; the pupa breathes through a pair of respiratory trumpets (breathing siphons) on its thorax.Answer:Option B (siphon)