单选题 Wisdom in old age depends on a fresh supply of new brain cells, a study in mice suggests.. When mature mice learn a new task, their newly generated brain cells are three times more active than their old ones, the researchers found. The findings add to a growing body of evidence that the adult brain needs a steady addition of new cells to maintain its mental faculties.
Researchers found that mature mice's brain cells are much more active than before when

• A. they are transplanted with new brain cells.
• B. they learn to do something new.
• C. they gain weight in the body.
• D. they get new cells from other mic