Final answer:
GRB2 is part of the signaling pathways associated with EGFR and functions as an adapter protein, not as a kinase, guanine nucleotide exchange factor, or protease.
Step-by-step explanation:
GRB2 is an important protein that functions in signal transduction pathways. It is known to play a critical role during cell signalling, especially when it is associated with receptor tyrosine kinases like the epidermal growth factor receptor (EGFR).
Upon the binding of epidermal growth factor (EGF) to EGFR, GRB2 associates with the receptor through its SH2 domain along with another protein called SOS, which is a guanine nucleotide exchange factor. GRB2 itself is not a kinase, a guanine nucleotide exchange factor, nor a protease. Therefore, the correct answer is: GRB2 is a c. adapter protein.