我国交通法规明确禁止酒后驾车。交通警察使用的一种酒精检测仪中装有重铬酸钾（K₂Cr₂O₇），它对酒精非常敏感，该化合中铬元素（Cr）的化合价为

    A dog has a piece(片) of meat in his mouth. He sees himself(他自己) in the water. He thinks it is another dog. That dog has a piece of meat in his mouth，too. He wants to get(得到) his meat. Then he can have two pieces. He opens his mouth to bark(吠叫) and his meat goes down into(在……里面) the water.

下面几个比例尺中，最大的是（　　）

假设某植物种群非常大，可以随机交配，没有迁入和迁出，基因不产生突变。抗病基因T对感病基因t为完全显性。现种群中感病植株tt占2/9，抗病植株Tt占4/9，抗病植株可以正常开花和结实，而感病植株在开花前全部死亡。则子一代中能稳定遗传的抗病植株占（）