**Core Concept**
In the context of a preterm infant exhibiting jitteriness, irritability, difficulty feeding, coarse tremors, high-pitched cry, and gastrointestinal symptoms such as diarrhea and emesis, the clinical presentation is suggestive of neonatal abstinence syndrome (NAS) due to maternal opioid use during pregnancy.

**Why the Correct Answer is Right**
Maternal opioid use, particularly with heroin, leads to the transfer of opioids across the placenta, resulting in fetal exposure to these substances. After birth, the infant experiences withdrawal symptoms as the opioid levels drop. The symptoms exhibited by the infant, such as jitteriness, irritability, and tremors, are classic signs of opioid withdrawal. The gastrointestinal symptoms, including diarrhea and emesis, are also indicative of opioid withdrawal.

**Why Each Wrong Option is Incorrect**
**Option A:** Alcohol withdrawal in a neonate typically presents with symptoms such as tremors, irritability, and poor feeding, but the gastrointestinal symptoms like diarrhea and emesis are less common.

**Option B:** Marijuana withdrawal in a neonate is not well-characterized, and the clinical presentation is often nonspecific, making it a less likely diagnosis.

**Option D:** Cocaine withdrawal in a neonate is also not well-characterized, and the clinical presentation is often nonspecific, making it a less likely diagnosis.

**Clinical Pearl / High-Yield Fact**
Neonatal abstinence syndrome (NAS) is a leading cause of hospital readmission in the neonatal period, with an estimated 5-10% of infants born to opioid-dependent mothers experiencing NAS.

**✓ Correct Answer: C. Heroin. Heroin withdrawal in a neonate.**