sentence: Clouds are classified according to how they look and how high the base of the cloud is in the sky.
sentences_after: This system was suggested in 1802. There are different sorts of clouds because the air where they form can be still or moving forward or up and down at different speeds. Very thick clouds with large enough water droplets can make rain or snow, and the biggest clouds can make thunder and lightning.
concept_name: cloud
headings: Cloud Cloud classification
categories: Basic English 850 words