## **Core Concept**
The detection of fetal parts or fetal pas by X-ray involves understanding the timeline of fetal development and bone ossification. Fetal development is a critical aspect of embryology and obstetrics, where various milestones can be identified through imaging techniques.

## **Why the Correct Answer is Right**
Fetal bones start to ossify and become visible on an X-ray after a certain period of gestation. Typically, fetal bones can be detected on an X-ray by around 14-16 weeks of gestation. This timeframe allows for the ossification of the long bones and other skeletal structures to progress to a point where they are visible on radiographic imaging. Therefore, the correct answer, which corresponds to this timeframe, is right because it accurately reflects the period when fetal pas (parts) become visible on an X-ray.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests an earlier timeframe than typically required for fetal bones to be visible on an X-ray. At this early stage, the bones may not have ossified sufficiently to be detectable.
- **Option B:** Similarly, this option might be too early for reliable detection of fetal parts through X-ray, given the variability in fetal development and the degree of bone ossification.
- **Option D:** This option suggests a later timeframe, which, while potentially allowing for the detection of fetal parts, is not the earliest point at which detection becomes feasible.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the ability to detect fetal parts on an X-ray depends on the degree of bone ossification, which progresses with gestational age. Clinically, ultrasound is now the preferred method for assessing fetal development due to its safety and ability to provide detailed images without radiation exposure. However, knowing the timeline for X-ray detection is crucial for understanding fetal development milestones.

## **Correct Answer:** C. 14-16 weeks.