If only high, thin cirrus clouds are present, why is heavy surface rainfall unlikely?

Correct answer: They are generally thin ice-crystal clouds with limited precipitation particle growth

Direct answer: B is correct. Cirrus clouds occur at great heights and are usually thin, wispy clouds made mainly of ice crystals because the air there is very cold. Their small amount of condensed material and delicate structure generally do not provide the strong, sustained growth of precipitation particles needed for heavy rain to reach the ground. Some high clouds may indicate changing weather, but the presence of cirrus alone does not mean that heavy surface rainfall is occurring. A is wrong because clouds are not made of rock. C is wrong because cirrus clouds are high in the atmosphere, not at the ground; a cloud at ground level is fog. D is wrong because cirrus clouds do not always produce hail, and hail normally requires strong vertical currents and suitable freezing conditions in a storm cloud. Memory cue: cirrus means high and wispy; thick, deep clouds are more likely to produce heavy precipitation.