Vertex presentation (flexion of the fetal head) is the optimal presentation for passage through the birth canal.Option B: Transverse lie is an unacceptable fetal position for vaginal birth and requires a C-section.Option C: Frank breech presentation. in which the buttocks present first. can be a difficult vaginal delivery.Option D: Posterior positioning of the fetal head can make it difficult for the fetal head to pass under the maternal symphysis pubis.