Analyze the part–whole pattern: “Bone : Skeleton : Nerve”. Select the option that mirrors “part : whole : part” for the same whole.

Introduction / Context:
Triad structure questions test whether you can infer the hidden relationship among three items and find another triad with the same structure. In “Bone : Skeleton : Nerve”, “skeleton” is a bodily whole or framework, while “bone” and “nerve” are parts of the body. The intended structure is “part : whole : part” where the first and third are components associated with the same named whole/body system context.

Given Data / Assumptions:
The stem suggests a whole (skeleton/body framework) flanked by two parts (bone and nerve) viewed at the body level.

Concept / Approach:
We need an option where the middle is a whole and both flanking terms are parts of that very whole. “Retina : Eye : pupil” fits perfectly: the eye is the whole; retina and pupil are parts of the eye. This mirrors the structural idea even if the biological systems differ (skeletal vs visual). The key is preserving the “part–whole–part” configuration.

Step-by-Step Solution:

Verification / Alternative check:
“House : Door : Window” is also part–whole–part but not anatomical; typical exam keys prefer anatomical parity when the stem is biological. “Spoke : Wheel : Handle” breaks the common whole (handle is not part of a wheel). “Snow : Cloud : Ice” mixes states/materials rather than parts of a single whole.

Why Other Options Are Wrong:
They fail to maintain a single, consistent whole with both flankers as its parts.

Common Pitfalls:
Focusing on topical similarity rather than structural mapping; structure is decisive here.

Final Answer:
Retina : Eye : pupil