Concept:Dry-bulb and wet-bulb thermometer readings show how much moisture is in the air.Explanation:The wet bulb is cooled by evaporation of water from its muslin covering.If the air is dry, evaporation is rapid, so the wet-bulb reading becomes much lower than the dry-bulb reading.Therefore, a large difference between the two readings means the air contains little water vapour.Answer:A. there is little water vapour in the air