**Core Concept**
The question is testing the ability to identify a drug that can cross the placenta, which is crucial in prenatal and perinatal medicine. This involves understanding the pharmacokinetics and pharmacodynamics of various drugs, particularly their ability to pass through the placental barrier.

**Why the Correct Answer is Right**
Drugs that are lipid-soluble or have a low molecular weight can cross the placenta. This is because the placenta is a lipid-rich membrane that allows lipophilic substances to diffuse through it. The correct answer is a drug that is known to have these characteristics. Additionally, the placental barrier is more permeable to certain drugs, such as those that are weak bases or have a higher lipid solubility. The correct answer is a good example of a drug that meets these criteria.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a polar molecule that is not lipid-soluble, making it less likely to cross the placenta.
**Option B:** This option is incorrect because it is a large molecule that is not able to diffuse through the placental barrier.
**Option C:** This option is incorrect because it is a drug that is primarily excreted through the kidneys and is not typically associated with placental transfer.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that not all drugs that cross the placenta are teratogenic, but many can cause fetal harm if taken during pregnancy. Always consider the potential risks and benefits of medication use in pregnant patients.

**Correct Answer: D. Digoxin ( Lanoxin)**