**Core Concept**
The underlying principle being tested is the management of **bradycardia** induced by **beta blocker overdose**. This condition involves the inhibition of **beta-adrenergic receptors**, leading to decreased heart rate.

**Why the Correct Answer is Right**
In the case of beta blocker overdose, the treatment aims to counteract the effects of the excess beta blockers on the heart. The most effective approach is to administer a drug that can directly stimulate the heart, bypassing the blocked beta receptors.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not the first-line treatment for beta blocker-induced bradycardia.
**Option B:** Incorrect as it is not typically used for this specific condition.
**Option C:** Incorrect because, although it has some effects on the heart, it is not the preferred choice for beta blocker overdose.
**Option D:** Incorrect as it does not directly address the cause of the bradycardia.

**Clinical Pearl / High-Yield Fact**
In cases of beta blocker overdose, **glucagon** is a high-yield fact to remember as it can stimulate the heart directly, providing a rapid increase in heart rate.

**Correct Answer:** D. Glucagon