1. The fertility of the US had been declined since the end of the post-world war II baby boom. 
2. In the mid-1970s, a 40% plurality of mothers had given birth four or more children 

3. Just 14% of the mothers have four or more children now, as a result, smaller family 
4. At the same time, the share of  mothers from the ages 40 to 44 who have only one child has doubled 
5. The share of mothers who have three children remains virtually unchanged 
//Bài này mình làm tương đối thôi nha//