= Solution
The healthy sample establishes the basal and normal stimulated patterns for the same <cell type> and handling conditions. Sample A contains bands around $96$ and $30\,\mathrm{kDa}$ in both conditions; <PDGF> additionally induces bands near $73$, $62$ and $44$–$45\,\mathrm{kDa}$. These are compatible, respectively, with stimulated <Raf>, <Akt> and unresolved <MEK>/<ERK> signals, given the supplied masses. \b[Ligand-dependent appearance of those bands is the normal comparison for suspected constitutive signaling.] Their identities remain provisional until confirmed with target-specific reagents. The unchanged bands are useful internal observations but cannot be assumed to be validated loading controls merely because their intensities look similar.
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