题目

Mother made a promise ____ I passed the college entrance examination she would buy me a mobile phone. A. that   B. if that   C. that if   D. that whether 答案：C 解析: 名词promise后是同位语从句，用that引导；if引导条件状语从句。把铭牌为“6V 3W”小灯泡接在9V电源上，为使它正常发光，需要串联一个多大的电阻？