阅读下列短文，从每题所给的四个选项(A、B、C和D)中选出最佳选项。
A

"Motherhood may make women smarter and may help pr dementia(痴呆) in old age by bathing the brain in protective hormones," US researchers reported on Thursday. Tests on rats show that those who raise two or more litters of pups do considerably better in tests of memory and skills than rats who have no babies, and their brains show changes that suggest they may be protected against diseases such as Alzheimer’s dementia (早老痴呆症). University of Richmond psychology professor Craig Kinsley believes his findings will translate into humans. "Our research shows that the hormones of pregnancy (怀孕) are protecting the brain, including estrogen (雌激素), which we know has many neuroprotective (保护神经的) effects," Kinsley said. "It’s rat data but humans are mammals just like these animals are mammals," he added in a telephone interview. "They go through pregnancy and hormonal changes." Kinsley said he hoped public health officials and researchers would look to see if having had children protected a woman from Alzheimer’s dementia and other forms of age-related brain decline. "When people think about pregnancy, they think about what happens to the baby and the mother from the neck down," said Kinsley, who presented his findings to the annual meeting of the Society of Neuroscience in Orlando, Florida. "They do not realize that hormones are washing on the brain. If you look at female animals who have never gone through pregnancy, they act differently to the young. But if she goes through pregnancy, she will sacrifice her life for her infant--that is a great change in her behavior that shows the genetic alterations(改变) to the brain. "

How do scientists know "Motherhood may make women smarter"