Step 1: Understanding the Concept: This question assesses knowledge of basic meteorological cloud classification.
Step 2: Detailed Explanation: Evaluating each statement regarding clouds:
(A) Clouds are classified according to their appearance and height. This statement is correct. The standard international cloud classification system uses Latin-based terms to group clouds by their form (e.g., cirrus, stratus, cumulus) and their altitude (high, middle, low).
(B) Cirrus clouds are high altitude clouds, which are usually feathery shaped and composed entirely of ice crystals. This is a correct description. Cirrus clouds are thin, wispy, and found at high altitudes where temperatures facilitate their formation from ice crystals.
(C) Nimbostratus clouds are mid level clouds producing sporadic rain. This statement is largely correct. Nimbostratus clouds are typically found at low to middle altitudes and appear as dark, grey, featureless layers associated with continuous rain or snow, rather than sporadic showers. While "sporadic" may be slightly imprecise, the core classification as a mid-level rain-producing cloud is accurate.
(D) Altocumulus are the heap-like clouds having flat bases and rounded tops. This description more accurately defines Cumulus clouds. Altocumulus clouds are mid-level clouds appearing as white or greyish patches, often in layers or waves with a mottled, lumpy texture. The characteristic "heap-like clouds with flat bases and rounded tops" is the definition of low-level Cumulus clouds. Therefore, this statement is incorrect.
Statements (A), (B), and (C) are correct.
Step 3: Final Answer: The correct option identifies only the correct statements: (A), (B), and (C).