What is the passage mainly about?

There are many reasons why family life in Britain has changed so much in the last 50 years. The liberation of women in the early part of the 20th century and social and economic effects of World War Ⅱ had a great impact on traditional family life. Women became essential to industry and professions. During the war, they had worked in factories and proved their worth. Now with the loss of millions of men their service was indispensable to the nation.
    More recently great advances in scientific knowledge and particularly in medicine have had enormous social consequences. Children are better cared for and are far healthier. Infant death rate was low. Above all, parents now can plan the size of their family if they wish to by more effective means of birth control.
    Different attitudes to religion, authority and tradition generally have also contributed to changes in family life. But these developments have affected all aspects of society. It is particularly interesting to know that the concept of the family as a social unit has survived all these challenges.
13. What is the passage mainly about?
Why did British women become indispensable to industry after World War Ⅱ?
What remained unchanged in spite of all the challenges in family life?