According to Standard Professional Thinking,how Often Should Nurses Auscultate the Fetal

According to standard professional thinking,how often should nurses auscultate the fetal heart rate (FHR) ?

A) Every hour in the active phase of the first stage of labour in the absence of risk factors
B) Every 20 minutes in the second stage,regardless of whether risk factors are present
C) Before and after ambulation and rupture of membranes
D) More often in a woman's first pregnancy