18. If a mutation in the Ras gene creates an allele that encodes a mutant Ras protein with a non-functional GTPase, this mutant Ras A) cannot be activated, even when it should be, because it cannot exchange a GDP for a GTP. B) cannot be activated, even when it should be, because it can't phosphorylate its GDP to GTP. C) cannot inactivate itself because it can't exchange its GTP for GDP. D) cannot inactivate itself because it cannot dephosphorylate its GTP to GDP. E) cannot be activated because it can't dephosphorylate its GTP to GDP.