A:1+2Δx
B:2+Δx
C:3+2Δx
D:4+2Δx
When the new president ______ after the election, he _______ a series of new policies.
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( )