Answer: b. 5C (46.4F)
Step-by-step explanation:
When air that is not saturated rises, it cools at a rate of 10 °C per 1,000 m. The warm air parcel only became saturated at 1,000m so by then it had cooled by 10°C.
Temperature at 1,000 m = 21°C - 10°C
= 11°C
When air is saturated, it is generally assumed to cool at a rate of 6°C per 1,000m. From 1,000m to 2,000 metres the air parcel decreased by a further 6°C bringing its temperature to 5°C.