**Core Concept**
Buprenorphine is a partial agonist at the mu-opioid receptor (MOR) and an antagonist at the kappa-opioid receptor (KOR). It is used for the treatment of opioid use disorder and chronic pain management.

**Why the Correct Answer is Right**
Buprenorphine's partial agonist activity at the MOR leads to a ceiling effect, which prevents excessive respiratory depression and other opioid-related side effects. This partial agonism also results in a longer duration of action compared to full agonists like morphine. The antagonist activity at the KOR contributes to its analgesic effects and helps to reduce the risk of opioid-induced hyperalgesia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because buprenorphine is not a full agonist at the MOR, as it would produce excessive respiratory depression and other opioid-related side effects.
**Option B:** This option is incorrect because buprenorphine is not an antagonist at the MOR, as it would not provide any analgesic effects.
**Option C:** This option is incorrect because buprenorphine is not an agonist at the delta-opioid receptor (DOR), as its primary mechanism of action is through the MOR and KOR.

**Clinical Pearl / High-Yield Fact**
When using buprenorphine for opioid use disorder treatment, it's essential to consider the risk of precipitated withdrawal in individuals who are physically dependent on full opioid agonists. This can be mitigated by administering a loading dose of naloxone or clonidine.

**Correct Answer:** B. Partial agonist at MOR, antagonist at KOR.