**Core Concept**
Hofbauer cells are a type of macrophage found in the placenta, playing a crucial role in its development and function. These cells are involved in the regulation of trophoblast invasion, placental angiogenesis, and the clearance of debris and pathogens.

**Why the Correct Answer is Right**
Hofbauer cells are characterized by their unique morphology, with a large nucleus and abundant cytoplasm, and are typically found in the villous stroma of the placenta. They express various receptors and molecules, including CD68, CD163, and HLA-DR, which enable them to interact with neighboring cells and regulate placental function. Hofbauer cells also produce various cytokines and growth factors, such as VEGF and IL-6, which promote trophoblast invasion and angiogenesis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Hofbauer cells are not primarily involved in the regulation of fetal lung development.
**Option B:** This option is incorrect because Hofbauer cells are not a type of immune cell found in the liver.
**Option C:** This option is incorrect because Hofbauer cells are not associated with the regulation of fetal bone growth.

**Clinical Pearl / High-Yield Fact**
Hofbauer cells are a key component of the placental villous stroma and play a critical role in maintaining placental homeostasis. Abnormalities in Hofbauer cell function or number have been implicated in various pregnancy complications, including preeclampsia and intrauterine growth restriction.

**Correct Answer:** C.