一个DNA分子中有碱基A20个,占全部碱基的20%,若DNA连续复制2次,需要碱基G( )
A:40个
B:60个
C:90个
D:120个
Hello ! My name is LiQiang . There are four people in my family . My father is a worker . My mother is a farmer . My little sister is a pupil. I am a pupil , too . We are in the same school .
将一个金属块挂在弹簧测力计上,当金属块浸入液体中时弹簧测力计上的示数表示的是金属块所受到的( )