【正确答案】 C

【答案解析】[解析]
Nigeria"s Acting President Good luck Jonathan has [23]dismissed the country"s National Security Adviser Abdullahi Muktar Sarki after an ethnic violence that left hundreds dead at the weekend. The announcement was made after a special security meeting in the capital Abuja. And Aliyu Gisau, a retired general, will take the place. Earlier, police said they had restored order to three villages in the center of the country where the violence occurred.

[读题] 题干表明，本题是问尼日利亚的国家安全顾问被解雇的原因是什么。
题干中的fired对应原文的dismissed。由原文中提到的...has dismissed the country"s National Security Adviser ...after an ethnic violence that left hundreds dead at the weekend可知，国家安全顾问被解雇的原因与一起暴力事件有关，而该暴力事件造成了数百人死亡，故答案为C)。