Classification — find the set where all three items belong to the same type: Which option contains three items from one clear category?

Introduction / Context:
Among four mini-lists, only one groups three members of a single, precise category. A fast technique is to annotate each term with its everyday category (device, animal, money unit, measurement unit, etc.) and select the option that yields three identical labels. Be careful with distractors that sneak in a “category word” (like “Currency”) next to two members, breaking uniformity.

Given Data / Assumptions:

• Hertz, Calorie, Watt — all are measurement units (frequency, energy, power).
• Keyboard, Mouse, Category — two computer input devices + a meta-term “Category” (not a device).
• Leveret, Cub, Elephant — two names for young animals (leveret = young hare; cub = young of certain mammals) + Elephant (adult animal/species); not uniform.
• Yen, Pound, Currency — two named currencies + the generic class “Currency”; mixing instance names with the class term.

Concept / Approach:
Uniform category means all three are peers under the same super-type. Option D satisfies this cleanly: three peer measurement units. Options A–C each blend in a non-peer (a meta-category, a different life stage, or a class label), which violates the uniformity rule.

Step-by-Step Solution:
1) Label D: unit/unit/unit → uniform.2) Label A: device/device/meta-term → mixed.3) Label B: juvenile-term/juvenile-term/adult species → mixed.4) Label C: currency-name/currency-name/class-word → mixed.

Verification / Alternative check:
Attempt the sentence frame: “All three are types of _____.” Only D completes unambiguously as “measurement units.” The others fail or become awkward (“All three are types of… things?”), indicating non-uniformity.

Why Other Options Are Wrong:
Each includes at least one element that is not a peer in the intended category (meta-class words or mismatched stages).

Common Pitfalls:
Mistaking “Yen, Pound, Currency” as uniform because all relate to money. The presence of the generic class word ruins peer uniformity.

Final Answer:
Hertz, Calorie, Watt