**Core Concept**
The American Heart Association (AHA) and American College of Cardiology (ACC) jointly update guidelines for cardiopulmonary resuscitation (CPR) every 5 years. These guidelines provide evidence-based recommendations for healthcare providers to manage cardiac arrest situations effectively. The 2005 AHA/ACC guidelines introduced significant changes in CPR techniques, including the recommended number of chest compressions.

**Why the Correct Answer is Right**
According to the 2005 AHA/ACC guidelines, the recommended compression-to-ventilation ratio is 30:2 for adult CPR, with 30 chest compressions followed by two breaths. This change aimed to improve blood circulation and oxygenation during CPR, increasing the likelihood of successful resuscitation. The guidelines emphasized the importance of uninterrupted chest compressions to maintain cardiac output and prevent hypotension.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the 2005 AHA/ACC guidelines did not recommend a 15:2 compression-to-ventilation ratio. Although this ratio is used in some pediatric CPR guidelines, it is not applicable to adult CPR as per the 2005 guidelines.
**Option B:** This option is incorrect because the 2005 AHA/ACC guidelines did not recommend a compression-to-ventilation ratio of 15:15 for adult CPR. This ratio may be used in certain situations, but it is not the standard recommended by the 2005 guidelines.
**Option C:** This option is incorrect because the 2005 AHA/ACC guidelines do not recommend a compression-to-ventilation ratio of 30:1 for adult CPR. This ratio is not supported by evidence and may lead to inadequate ventilation during CPR.

**Clinical Pearl / High-Yield Fact**
A key takeaway from the 2005 AHA/ACC guidelines is the importance of maintaining a high-quality chest compression rate of 100-120 compressions per minute. This ensures optimal cardiac output and increases the chances of successful resuscitation.

**Correct Answer: C. 30:2**