我校每个班的教室都安装有投影仪，投影仪的镜头相当于____ 透镜，它对光线有____ 作用（填“会聚”或“发散”），它投射到屏幕上的光线所成的像是____ 像（填“实”或“虚”）．
生物的遗传和变异是通过____和____而实现的．
I cannot listen to both of you at the sametime. Please talk one after another.
