## Core Concept
The question tests knowledge of vaccine administration during pregnancy, focusing on live attenuated vaccines versus inactivated or subunit vaccines. Live vaccines are generally contraindicated in pregnancy due to the theoretical risk of transmission of the vaccine virus to the fetus.

## Why the Correct Answer is Right
The correct answer, **D. BCG (Bacillus Calmette-Guérin)**, is a live attenuated vaccine. Live vaccines, such as BCG, pose a theoretical risk to the fetus, making them contraindicated during pregnancy. In contrast, inactivated vaccines or subunit vaccines are generally considered safe.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is not provided, but typically, inactivated vaccines like Hepatitis A and B, and Tdap (tetanus, diphtheria, and pertussis) are recommended during pregnancy.
- **Option B:** Similarly, this option is not provided, but if it were an inactivated vaccine or a subunit vaccine, it would likely be safe during pregnancy.
- **Option C:** Without the specific option, we assume it's another type of vaccine; if it's an inactivated or subunit vaccine, it's likely safe.

## Clinical Pearl / High-Yield Fact
A key point to remember is that live vaccines, such as **BCG**, **MMR (measles, mumps, and rubella)**, and **varicella**, are generally avoided during pregnancy. Inactivated vaccines, like **influenza** and **Tdap**, are recommended to protect against serious diseases.

## Correct Answer: D. BCG (Bacillus Calmette-Guérin)