题目

--You did wrong , you should call him up first .  --- _________But I’ll try.       A. I am sorry to hear that   B. It’s not easy    C. You, first .      D. Forget about it 答案：B7．矮秆不抗病小麦与高秆抗病小麦杂交，获得了矮秆抗病新品种．该育种过程所依据的遗传学原理是（　　）A．基因突变B．染色体数目变异C．基因重组D．染色体结构变异