Which of the following combinations correctly identifies the cloud types that are commonly known as rain clouds because they are capable of producing significant precipitation?

Introduction / Context:
Understanding different types of clouds is a basic part of geography and meteorology. Some clouds are mainly decorative high level formations, while others are powerful rain bearing systems. This question asks which combination of cloud types is commonly associated with rainfall, making it important for weather prediction and climate related general knowledge.

Given Data / Assumptions:

• The cloud types listed include Cirrus, Nimbostratus, Cumulonimbus, and Altocumulus.
• The term rain cloud refers to clouds that usually produce measurable precipitation over an area.
• The question allows multiple statements but asks for the correct combination among the options.
• Only one option groups together the main rain bearing types.

Concept / Approach:
Nimbostratus and Cumulonimbus are the classic rain bearing clouds. Nimbostratus is a thick, layered cloud that produces steady, widespread rain or snow. Cumulonimbus is a tall, towering cloud associated with thunderstorms, heavy showers, lightning, and sometimes hail. Cirrus clouds are high, wispy clouds that do not bring significant rain, and Altocumulus are mid level clouds that usually produce little or no rainfall at the ground. Therefore, the correct combination is Nimbostratus and Cumulonimbus.

Step-by-Step Solution:
Step 1: Recall that the prefix nimbo or nimbus is associated with precipitation.Step 2: Recognise that Nimbostratus forms thick, dark layers, covering the sky and producing continuous rain.Step 3: Remember that Cumulonimbus grows vertically and produces showers and thunderstorms.Step 4: Note that Cirrus clouds are high, thin, and mainly indicate fair weather or changes, not heavy rain.Step 5: Altocumulus are mid level patchy clouds with limited precipitation. Thus, the correct rain cloud combination is Nimbostratus and Cumulonimbus only.

Verification / Alternative check:
Geography textbooks describe Nimbostratus as the main cloud for continuous rain and Cumulonimbus as the thunderstorm cloud. They specifically mention that Cirrus and most Altocumulus clouds do not produce much rain at the surface. Cross checking this classification with the options shows that only the combination of Nimbostratus and Cumulonimbus fits the definition of rain cloud.

Why Other Options Are Wrong:
Option A: Cirrus is a high, wispy cloud with little or no rainfall, so pairing it with Nimbostratus is partly incorrect.Option C: Altocumulus is usually not a strong rain producer; combining it with Cumulonimbus does not give a fully correct rain cloud pair.Option D: Cirrus and Altocumulus together are mainly non rain clouds.Option E: Cirrus does not belong in the main rain cloud category even though Cumulonimbus does.

Common Pitfalls:
Students sometimes assume that any large or impressive looking cloud must be a rain cloud, or they focus only on the word cumulonimbus and forget about nimbostratus. Another pitfall is ignoring the nimbo or nimbus prefix, which is a strong clue for rain bearing clouds. Remembering both nimbostratus and cumulonimbus as key rain clouds helps answer such questions correctly.

Final Answer:
The correct answer is Nimbostratus and Cumulonimbus only.