At 35 Weeks of Pregnancy,a Woman Experiences Preterm Labor

At 35 weeks of pregnancy,a woman experiences preterm labor.Although tocolytic medications are administered and she is placed on bed rest,she continues to experience regular uterine contractions and her cervix is beginning to dilate and efface.What is an important test for fetal well-being at this time?

A) Percutaneous umbilical blood sampling (PUBS)
B) Ultrasound for fetal size
C) Amniocentesis for fetal lung maturity
D) Non stress test (NST)