Final answer:
Medium-altitude clouds can cause light rain and snow, since they often contain both water droplets and ice crystals that lead to precipitation when they grow large enough around nuclei like dust particles.
Step-by-step explanation:
The correct answer to the question about the characteristics of clouds at medium altitudes is option B: They cause light rain and snow. Medium-altitude clouds, which are usually classified as altostratus or altocumulus clouds, can consist of both water droplets and ice crystals. These clouds are primarily responsible for producing light precipitation including rain and snow, which depends on the temperature within the cloud and at the surface level. It is the process of condensation and the growth of these water droplets around particles such as dust or ice crystals that can lead to precipitation. Clouds at these altitudes do not generally produce severe weather or lightning. Severe weather and lightning are more associated with cumulonimbus clouds, which are typically found at lower altitudes.