Penicillin and Many Other Antibiotics Are β-Lactams

Penicillin and many other antibiotics are β-lactams. What is the composition of the β-lactam ring?

A) 1 carbon atom and 3 nitrogen atoms
B) 2 carbon atoms and two nitrogen atoms with the carbon atoms adjacent
C) an alternating sequence of 2 carbon atoms and two nitrogen atoms
D) 3 carbon atoms and one nitrogen atom