Answer:
c) Nimbus
Step-by-step explanation:
Stated on the Essay of Modifications of Clouds in 1803 by Luke Howard, there is a special rainy cloud category that combines the three forms of clouds Cumulo+Cirro+Stratus, called 'Nimbus', an ancient Latin word that means Rain or Rain Storm.
The majority of precipitation comes from nimbus clouds, this clouds have the greatest vertical height and tend to appear dark gray because their depth and density of water droplets.