Step 1: Understanding the Concept:
Cow, buffalo, goat, and sheep are all domestic animals.
They share some common characteristics.
Step 2: Key Formula or Approach:
No specific formula.
Need to understand the classification of these animals.
Step 3: Detailed Explanation:
All four are herbivores (eat plant material).
All four are mammals (give birth to young, have mammary glands).
However, the question asks for the similarity.
They are all herbivores AND mammals.
But the option "All are mammals" is more fundamental.
They are not carnivores or omnivores.
Thus, the common similarity is that all are mammals.
Step 4: Final Answer:
Cow, buffalo, goat, and sheep are all mammals.
Hence, the correct option is (D).