Identifying upper limb bones from anatomical positions

Steps:

• Locate X in the shoulder girdle, which connects the arm to the trunk.
• Identify Y in the forearm, medial to the radius and forming the elbow hinge.
• Compare options: scapula fits shoulder, ulna fits medial forearm.
• Eliminate mismatches in bone positions.

Why D is correct:

• Scapula forms the shoulder blade (X), and ulna is the longer medial forearm bone (Y), per standard human anatomy.

Why the others are wrong:

• A: Humerus is upper arm (not shoulder), radius is lateral forearm.
• B: Both humerus (upper arm) and ulna (forearm) mismatch X's shoulder position.
• C: Scapula fits X, but radius is lateral forearm, not medial like Y.

Final answer: D