The correct answer is option 1 - Cirrus clouds are composed of ice crystals. Cirrus clouds are high-altitude clouds that generally appear as thin, wispy strands. They are made of ice crystals because they form at heights where the air is typically below the freezing point of water.

Option 2 involves a common misconception. Cirrus clouds do not have a flat base and an appearance of rising domes. That is an attribute associated with cumulus clouds, which have defined edges and can tower high into the atmosphere.

Option 3 is incorrect too, as it mixes up two different types of clouds. Cumulus clouds are not white and thin with a fibrous, feathery appearance. That description corresponds to cirrus clouds. Cumulus clouds are puffy-looking and may resemble cotton balls.

Option 4 is wrong because cumulus clouds aren`t classified as high clouds. They form usually at lower to middle levels of the atmosphere. High clouds typically include types like cirrus.