Final answer:
The nurse should first check the fetal heart rate.
Step-by-step explanation:
When a client in active labor suddenly shouts, 'I have to push! I have to push!' and the nurse determines that the client is 8 cm dilated, the first action the nurse should take is to check the fetal heart rate (d). This is because a sudden urge to push can indicate that the baby is descending into the birth canal, and checking the fetal heart rate will help ensure the well-being of the baby.