A、They can last for at least two years. B、They can last for at most two years. C、The scale of them is larger than that of adoles

Scans of 25 first-time moms showed these structural brain changes lasted for at least two years after giving birth. European researchers said the scale of brain changes during pregnancy were similar to those seen during adolescence.
    But they found no evidence of women’s memory deteriorating.
    Many women have said that they feel forgetful and emotional during pregnancy and put it down to "pregnancy" or "baby" brain—and, it seems, with good reason.
    Pregnancy is characterized by extreme rise of sex hormones and involves drastic physiological and physical changes in the body, the researchers say.
    During those nine months, women experience a flood of estrogen which is greater than for the whole of the rest of their lives.
    Yet research on the effects of pregnancy on the human brain is scarce.
    This study, from researchers at the Universitat Autonoma de Barcelona and Leiden University and published in Nature Neuroscience, looked at the brain scans of women before they became pregnant, soon after they gave birth, and two years later, to see how the brain changed.
    And they compared these women’s brains with those of 19 first-time fathers, 17 men without children and 20 women who had never given birth. The researchers found substantial reductions in the volume of grey matter in the brains of first-time mothers.
    The grey matter changes occurred in areas of the brain involved in social interactions used for attributing thoughts and feelings to other people—known as " theory-of-mind" tasks.
    The researchers thought this would give new mothers an advantage in various ways—help them recognize the needs of their children, be more aware of potential social threats and become more attached to their babies.
    Questions 19 to 22 are based on the recording you have just heard.
    19.What can we learn about the brain changes in first-time moms?
    20. Which is an obvious character of pregnancy according to the researchers?
    21.What did the researchers at the Universitat Autonoma de Barcelona and Leiden University find?
    22.How would grey matter changes benefit new mothers according to the researchers?