**Core Concept**
Vacuum extraction is a method of assisted vaginal delivery where a vacuum device is applied to the fetal head to facilitate delivery. It is typically used when the mother is experiencing difficulty with the second stage of labor, and the cervix is fully dilated.

**Why the Correct Answer is Right**
The correct answer is B. BE because vacuum extraction can be used in incompletely dilated cervix, but not in a non-dilated cervix. Incompletely dilated cervix means the cervix is not fully open, but vacuum extraction can still be applied to facilitate delivery. However, applying vacuum extraction in a non-dilated cervix can lead to complications such as cervical tear or laceration. Option B is correct because vacuum extraction can be used in cases where the cervix is not fully dilated, but still accessible for the vacuum device. Option E is correct because the vacuum device is typically applied 3 cm anterior to the posterior fontanel, which is the soft spot on the back of the baby's head.

**Why Each Wrong Option is Incorrect**
* **Option A:** Vacuum extraction cannot be used in a non-dilated cervix because it increases the risk of cervical tear or laceration.
* **Option C:** Vacuum extraction is not typically used in face presentation because it can cause injury to the baby's face.
* **Option D:** Applying the vacuum device 3 cm post to anterior fontanel is incorrect because it is not the correct location for the application of the vacuum device.

**Clinical Pearl / High-Yield Fact**
When using vacuum extraction, it is essential to assess the cervix for dilation and the fetal head for position before applying the device. The vacuum device should be applied 3 cm anterior to the posterior fontanel to avoid injury to the baby's head.

**✓ Correct Answer: B. BE. Both B and E are correct.**