【简答题】20 世纪70年代,第一位访问中国的美国总统是()。
【单选题】Standing among the students ________ together with their English teacher.
【单选题】听力原文:(A) He is wearing a cape. (B) He is holding up a sign. (C) He is standing on a stage. (D) He is waiting to cross the street.
【判断题】当导体中有交流电或者交变电磁场时,电流集中在导体外表的薄层,越靠近导体表面,电流密度越大,导线内部实际上电流较小,该描述是否正确