Okay, I need to figure out the correct answer for the question about where a bone marrow biopsy is done in an infant. Let me start by recalling what I know about bone marrow biopsies in children.

First, the core concept here is the anatomical site for bone marrow aspiration and biopsy in infants. I remember that in adults, the iliac crest is the common site, but in children, especially infants, the site might be different. The options weren't given, but I can think of possible options. Common sites in children could be the sternum, tibia, or iliac crest. Wait, but for infants, maybe the tibia is the site because the iliac crest is not fully developed yet.

Let me verify. In infants and young children, the tibia is often used because the bone is more accessible and the marrow is more readily available. The sternum is another option but might be less common. The iliac crest in infants might not be the best choice because the bone structure is different. So the correct answer would be the tibia, specifically the proximal tibia.

Now, for the incorrect options, if someone thought the iliac crest is used, that's more for adults. The sternum is another possible site but not the primary one in infants. The femoral site might be considered but less common.

The clinical pearl here is that in infants, the tibia is preferred due to the ease of access and the presence of active marrow. Also, the sternum is avoided in some cases because of the risk of injury. So the key point is the tibia for infants.

Putting it all together, the correct answer should be the tibia, and the explanation needs to cover why the other sites are not suitable. The core concept is the anatomical site for bone marrow biopsy in infants.

**Core Concept**
Bone marrow biopsy in infants is performed at a site with accessible and active marrow. The **proximal tibia** is preferred due to its large medullary cavity and less ossified structure compared to adult sites like the iliac crest.

**Why the Correct Answer is Right**
In infants, the **tibial tuberosity** (proximal tibia) is the standard site for bone marrow aspiration and biopsy. This area has abundant red marrow and a relatively thin cortex, allowing easier needle insertion. The iliac crest is typically used in older children and adults, while the sternum is avoided in infants due to anatomical constraints and risk of injury.

**Why Each Wrong Option is Incorrect**
**Option A:** *Sternum* – Incorrect. Though used in older children/ adults, the sternum is not preferred in infants due to its thinness and proximity to vital structures.
**Option B:** *Iliac crest* – Incorrect. This is the adult site but less viable in infants because of underdeveloped iliac bone and limited marrow access.
**Option C:** *Femoral shaft* – Incorrect. The femur is rarely used due to technical difficulty and risk of damaging growth plates in children.

**Clinical Pearl / High-Yield Fact**
Never assume adult biopsy sites apply to infants. For children under 2 years, the **proximal tibia** is the gold standard for bone marrow procedures. Remember: **Tibia for Tiny Ones** (T4T2) to avoid unnecessary complications.

✓ Correct Answer: C. Tibia