Final answer:
Nifedipine option (B) is the medication used as a tocolytic agent to suppress preterm labor, by relaxing the smooth muscles in the uterus and inhibiting contractions.
Step-by-step explanation:
The drug commonly used as a tocolytic agent to suppress preterm labor is B. Nifedipine. Tocolytic agents are medications given to delay preterm labor, providing additional time for the fetus to develop and reducing the risks associated with preterm birth. Nifedipine is a calcium channel blocker that relaxes the smooth muscles in the uterus to inhibit contractions.
Oxytocin is the hormone primarily responsible for the contractions during labor, not a tocolytic agent. As for the other drugs listed, Ibuprofen and Acetaminophen are nonsteroidal anti-inflammatory drugs (NSAIDs) used for pain relief and inflammation but not for tocolysis, and Ceftriaxone is an antibiotic used for bacterial infections.