[单选题]
The mass of an atom iohl;vx. 3xjojsz+g /+: ex8zt suisf+ o7i( l76u9 kznnpu6d9w
A. approximately equally divided between neutrons, protons, and electrons.
B. evenly divided between the nucleus and the surrounding electron cloud.
C. concentrated in the cloud of electrons surrounding the nucleus.
D. concentrated in the nucleus.
