请认真阅读下面短文，从短文后各题所给的A、B、C、D四个选项中，选出最佳选项。
   
    Humans are mammals（哺乳动物）．Most mammals are born able to do many things.
    Some can walk within a few minutes of being born. They have to be able to run away if 1is near. But human babies are born2. They need the care of adults to live.
    In the first month of life, babies cannot smile or sit up. They cannot even hold up their own heads3some help from grown-ups. 
    In the next few months, babies grow a lot. They learn to roll over, support their heads, and  4sit up while being held.
Babies also have to learn to use their5. It takes months for them to learn to reach for objects. At around six months old many babies can6an object from one hand to another.
    Babbling is7 a human baby learns to speak. Babies all seem to make similar sounds by babbling. They try to imitate (模仿) the sounds they hear from adults. It will take about nine months8a baby can say real words.
    Somewhere around a baby's first birthday he or she may stand or walk with help. Soon the baby will9around on his or her own!
    The first year of a baby's life is a time of growing and10. Growing sure takes a lot of work!