A.  56  the balance back to "yes”

B.help people  57  from depression and stress disorder

C.  58  they could

For decades, scientists have debates whether the cells was possibly in an area of the brain that is responsible for learning, memory and mood regulation.A growing body of research  59  ,but then a Nature paper last year raised doubts.Now, a new study  60  .

If the memory center of the human brain can grow new cells, it might  61  and offer new insights into memory and learning.If not, well then, it's just one other way people are different from rats and birds.