Which of the following is true of clouds at medium altitudes? a. they are the result of occluded fronts. b. they do not bring precipitation. c. they are composed mostly of liquid water. d. they are the cause of fog. (apex)

C. They are composed mostly of liquid water.

Explanation:

Medium altitude clouds form between 2000 to 6000 meters. They are majorly composed of liquid water or water droplets. When temperature is cold enough they can be composed of ice crystals too, specially in polar regions.  

They are usually of altocumulus and altostratus type. Altocumulus occurs in several layers and can appear as white or grey.It can be in form of sheets, patches or rolls.  Altostratus is greyish or bluish and generally indicates the arrival of rain. It partly or totally covers the sky.