This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T., Subject name: Medicine
In which of the following conditions smoking is protective? 
Select and explain. 
A. Ulcerative colitis, B. Crohn's disease, C. SLE, D. Alzheimer's
A: Ulcerative colitis
Answer: A: Ulcerative colitis 
Explanation: Ans. (a) Ulcerative colitisRef : Harrison 19th ed. /1952-53EPIDEMIOLOGY OF IBP Ulcerative colitisCrohn's diseaseMale/female ratio* 1:1* 1.1-1.8.1Smoking* May prevent disease* May cause diseaseOral contraceptives* No increased risk* Odds ratio 1.4Appendectomy* Protective* Not protectiveMonozygotic twins* 6% concordance* 58% concordanceDizygotic twins* 0% concordance* 4% concordance