题目

已知复数z=(a∈R）满足zi＞0或zi＜0，则a的值为（ ）A.3B.-3C.2或-3D.2 答案：解析:由zi＞0或zi＜0知zi为实数.∴=0且a2-3a-10≠0.∴a=2.答案:D用所给词的正确形式填空 He ________ (teach) English since 1970.