A:①②
B:③④
C:①④
D:②③
下列矿物中,能在所有物体上刻划出痕迹的是( )
——I can hardly believe my eyes. Is that you, Lucy?——Yes. It has been almost 20 years______ we were together.
人类能卷舌和不能卷舌是一对相对性状(控制该性状的基因用H或h表示).一对夫妇都能卷舌,他们生了一个不能卷舌的孩子.试推断这对夫妇的基因组成及再生一个能卷舌孩子的几率( )