Step 1: Use the HELPERR mnemonic to organise shoulder dystocia care: Help, Evaluate for episiotomy, Legs (McRoberts), Pressure (suprapubic), Enter manoeuvres, Remove posterior arm, Roll the patient.
Step 2: The first external pressure manoeuvre is suprapubic pressure, applied just above the pubic bone to nudge the wedged anterior shoulder beneath the symphysis. This is a frontline, effective and low-risk step, matching option B as the correct management.
Step 3: Contrast the alternatives. Flexing the hips onto the abdomen is the McRoberts position - useful but a different listed action. A fixed 90 degree posterior-shoulder rotation oversimplifies the internal rotational manoeuvres. Caesarean is reserved for failure of all manoeuvres, not the initial response once the head is out. Thus suprapubic pressure is the best answer.
\[\boxed{\text{Suprapubic pressure}}\]