51. Which description for receptor tyrosine kinases (RTK) is NOT correct? (A) RTKs is a family of plasma membrane receptors with protein kinase activity. (B) RTKs transduce extracellular signals through a mechanism similar to G protein-coupled receptors (GPCRs). (C) RTKs have a ligand-binding domain on the extracellular face of the plasma membrane. (D) RTKs have an enzyme active site on the cytoplasmic face.