Task: Question Answering
Input (English): 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.
Output (English): 4