**Core Concept**
Fetal membranes are critical structures that surround and protect the developing fetus during pregnancy. They include the amnion, chorion, and allantois, which play vital roles in fetal development, amniotic fluid production, and parturition.

**Why the Correct Answer is Right**
Fetal membranes are composed of the amnion, chorion, and allantois. The amnion is a thin, transparent membrane that encloses the amniotic fluid and fetus, while the chorion is a thicker membrane that separates the fetus from the uterine cavity. The allantois is a sac-like structure that connects the fetus to the placenta. These membranes work together to maintain the fetus's environment and facilitate its growth and development.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so we cannot evaluate it. However, we can proceed with the other options.
**Option B:** This option is not a fetal membrane, as it does not play a direct role in fetal development or protection.
**Option C:** This option is not a fetal membrane, as it refers to a different structure that is not directly involved in fetal protection or development.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that fetal membranes are critical for fetal development and protection. Complications in fetal membranes, such as preterm rupture of membranes, can lead to significant morbidity and mortality.

**Correct Answer: B. Amniotic fluid.**