In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Q: Question: Nitric oxide:
Options: <1> It is synthesized from methionine. <2> Activates cAMP-dependent protein kinase (PKA). <3> It binds to receptors coupled to G proteins (GPCR). <4> Induces relaxation of the vascular endothelium. <5> It binds to receptors with protein tyrosine kinase (PTK) activity.
A:
4