Option (A) Cirrus is correct because according to the textbook, Cirrus clouds are formed at high altitudes of 8,000 - 12,000 metres. In comparison, Cumulus clouds are formed at 4,000 - 7,000 m, while Nimbus clouds form at middle levels or very near the surface. Stratus clouds are layered clouds with no high altitude mentioned. Thus, Cirrus clouds occupy the highest position in the sky among all the given options.