— Is Jack on duty today?
— It_______ be him. It's his turn tomorrow.
A:mustn't
B:won't
C:can't
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( )
She found ____ difficult to settle and calm down in the ____ place, because she was worried about whether they would be discovered.