题目

在下列哪种情况下，生物能产生新的基因(    ) A．基因自由组合     B．基因互换     C．染色体数目变异       D．基因突变 答案：D----Did you _________ your friend when you were in Beijing?---No. But I _________ my aunt’s during my stay there.A．call on; called onB．call at; called atC．call on; called atD．call at; called on