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A
The part attached to the finger
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B
The part of the nail plate that extends beyond the fingertip
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C
The skin at the base
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D
The matrix
Why this is the answer
The free edge is the part of the nail plate that extends beyond the end of the finger and the nail bed. It is the portion that is shaped and filed during a manicure. (The matrix is the growth center; the nail bed is the skin under the attached plate; the cuticle/eponychium is at the base.) Correctly identifying the parts of the nail unit, including the free edge, is basic nail anatomy that supports proper manicure technique and is reliably tested on the exam.
Source: Skin & Nails — Free Edge