题目

26．—You look quite tired. —I __________ the project here in order to meet the deadline.        A．have done B．did    C．had done   D．have been doing 答案：A下图为基因型为Aa的生物自交产生后代的过程，基因的分离定律发生于（ ）Aa1A∶1a配子间的4种结合方式子代中3种基因型、2种表现型A．① B．② C．③ D．①②