Which of the following best describes how GPCR signaling pathways can be influenced?

• A. Neither external ligands nor internal proteins influence GPCR signaling.
• B. External ligands can activate GPCRs, while internal proteins can regulate the duration of signaling.
• C. Only external ligands can influence GPCR signaling pathways.
• D. Only internal regulatory proteins can influence GPCR signaling pathways.

Answer: (B)