Verification of truth: Milk necessarily contains which of the following? Choose the constituent that is always present.

Introduction / Context:
We identify a constituent present in all natural milk varieties. Processed variants (e.g., skim) alter proportions, so the attribute must remain true across types.

Given Data / Assumptions:

• “Milk” refers to natural mammalian milk (prior to dilution or dehydration).
• We compare universal vs. variable components.

Concept / Approach:
Milk is an emulsion/colloid consisting predominantly of water with dissolved lactose (milk sugar), minerals (including calcium salts), proteins, and dispersed fat globules. Some components vary by species and processing; water is fundamental.

Step-by-Step Solution:

Verification / Alternative check:
Across mammals and processing states, water’s presence is definitional for liquid milk.

Why Other Options Are Wrong:

• Sugar/Fats/Calcium: variable quantities; processing can reduce or modify presence/form.
• None of these: incorrect because water is always present in milk.

Common Pitfalls:
Taking “commonly present” (fat, lactose) as “necessarily present.”

Final Answer:
Water