Which of the following statements about molecular switches is false?
(a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.
(b) Protein kinases transfer the terminal phosphate from ATP onto a protein.
(c) Serine/threonine kinases are the most common types of protein kinase.
(d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.