— You spend too much time in front of the computer. You'd better away from it.
A:take a shower
B:take a sleep
C:take fl break
D:take some medicine
如图为田间豌豆种子萌发的初期,空气中的氧气浓度(x)与种子释放的CO2相对量(y)之间的关系曲线.a点说明( )