This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
Erythema nodosum is due to – a) Contraceptive pillsb) Barbituratesc) Penicillind) Sulphonamides 
Select and explain. 
A. b, B. ad, C. ac, D. ab
B: ad
Answer: B: ad 
Explanation: Causes of Erythema nodosum
Idiopathic
Bacterial: - Streptococci, TB, Leprosy (ENL), LGV, yersinia, mycoplasma, Rickettsia, Cat scratch disease.
Fungal: - Coccidioidomycosis, Histoplasmosis, Trichophyton.
Viral : - HBV, HIV
Drugs : - Sulfonamides, iodides, oral contraceptives.
Systemic diseases : - IBD (Ulcerative colitis, Crohn's disease), Sarcoidosis, Bechet's disease, SLF
Malignancy : - Hodgkin's disease, other malignancies
Other : - Pregnancy