Step 1: Understanding the Question:
The question asks which of the four listed cloud types is known as a rain producing cloud.
Step 2: Key Formula or Approach:
In cloud naming, the prefix or root "nimbo" or "nimbus" is used specifically for clouds that produce continuous, widespread precipitation. Other cloud names describe height and shape rather than rain producing ability.
Step 3: Detailed Explanation:
Nimbostratus is a thick, grey, low to middle level layer cloud that blocks out the sun and is the classic cloud that brings steady, continuous rain or snow over a wide area for hours.
Altocumulus is a mid level cloud made of small white or grey patches or rolls, it may sometimes signal a change in weather but does not itself produce rain.
Cirrostratus is a high, thin, ice crystal cloud that often creates a halo around the sun or moon, it is associated with fair to slightly worsening weather, not with rainfall.
Stratocumulus is a low, lumpy, patchy grey cloud layer that mostly brings overcast skies and at most light drizzle, it is not considered a true rain bearing cloud like nimbostratus.
Step 4: Final Answer:
The cloud type built specifically to carry and drop rain is nimbostratus, so option 1 is correct.