Correct Option: D

The clouds of the highest altitude are Cirrostratus. Cirrostratus cloud is a high, thin, generally uniform stratiform genus-type, composed of ice-crystals. It is difficult to detect and is capable of forming halos when the cloud takes the form of thin cirrostratus nebulosus. The cloud has a fibrous texture with no halos if it is thicker cirrostratus fibratus.