Did they meet John ? ______ .
A: Yes, they did .
B:No, he didn’t.
C:No, they did .
在巴斯德的曲颈瓶实验中,甲瓶的瓶口是竖直向上;乙瓶的瓶口是拉长呈S型的曲颈;将两个烧瓶内的肉汤同时煮沸放凉后,观察肉汤的变化.本实验的实验变量是( )
有四种物质:①细胞,②电子,③原子,④质子.按从大到小排列的顺序是 ( )