Which mechanism of labor occurs when the largest diameter of the fetal presenting part passes the pelvic inlet?

A. Engagement: Engagement occurs when the fetal presenting part, usually the biparietal diameter of the head, passes through the pelvic inlet and reaches the level of the ischial spines. This indicates that the widest part of the fetal head has entered the maternal pelvis, a key milestone in labor progression. B. Extension: Extension refers to the movement of the fetal head as it passes under the symphysis pubis during delivery, allowing the head to emerge from the birth canal. This occurs later in the second stage of labor, after engagement and descent. C. Internal rotation: Internal rotation is the turning of the fetal head to align with the maternal pelvic outlet, allowing passage through the mid-pelvis. It occurs after engagement and descent. D. External rotation: External rotation, or restitution, occurs after the fetal head is delivered, when it rotates to realign with the shoulders. This occurs late in the second stage of labor and is not related to initial engagement.