 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. 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.