Final answer:
The main advantage of PCA is that the client is actively involved in pain management.
Step-by-step explanation:
The main advantage of Patient-Controlled Analgesia (PCA) is that the client is actively involved in pain management. Option 4 is the correct answer. PCA allows the client to self-administer small doses of pain medication through an IV pump, giving them control over their pain relief. This empowers the client and allows them to customize their pain management according to their needs and comfort level.