**Core Concept**
Progress of labor can be monitored through various methods, but the most effective and widely accepted method is the assessment of cervical dilation and fetal station. This is crucial in determining the efficiency of labor and the need for interventions.

**Why the Correct Answer is Right**
The correct answer is **Cardiotocography (CTG)**. CTG is a graphical record of fetal heart rate and uterine contractions. It is the best monitoring method as it provides a continuous assessment of fetal well-being during labor. The fetal heart rate is analyzed for accelerations, decelerations, and variability, while the uterine contractions are evaluated for intensity and duration. This information helps in identifying potential complications, such as fetal distress, and guides the decision-making process for interventions.

**Why Each Wrong Option is Incorrect**
* **Option A:** Fetal scalp blood sampling is an invasive method used to assess fetal well-being, but it is not the best method for monitoring progress of labor.
* **Option B:** Ultrasound is used to assess fetal position and station, but it does not provide real-time information on fetal heart rate and uterine contractions.
* **Option C:** Electronic fetal monitoring (EFM) is similar to CTG but is not as sensitive in detecting changes in fetal heart rate and uterine contractions.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that CTG should be interpreted in conjunction with clinical assessment of the mother and baby, and not solely relied upon for decision-making.

**Correct Answer: D. Cardiotocography (CTG)**