阅读下面短文，掌握其大意，然后从各题所给的A、B、C和D项中，选出最佳选项。

      In the past，people usually believed what newly-born babies wanted was food and to be kept warm and dry．They thought babies were not able to 1things until they were five or six months old．2 the researchers in the United States now believe babies begin learning on their first 3 of life．They say babies are strongly 4 by their environment and one baby will 5 if his or her mother does something that the baby likes．

      A baby learns to get the best care possible by smiling to 6 her mother．This is how babies start to learn to 7 and communicate with other people．The researchers say this ability to learn 8 in a baby even before birth．They also 9 the idea that newly-born babies can 10 and understand sounds they heard while they were still 11 inside their mothers．

      Recently，an American study 12 112 babies found babies learned better when they were 13．The babies appeared to learn well whether they were sitting up on their own，sitting in seats or 14 to sit up．The researchers say keeping that kind 15 had what they called a 16 effect on the babies' ability to learn about objects．They say the body position may be linked to development in the 17．One 18 says babies can pay more attention to 19 an object if they do not have to be 20about their balance．