The correct version of these two sentences when combined is:
When we were in Europe on vacation, we usually flew on airplanes: however, sometimes we took the train.
We apply the semi-colon to indicate that they have different ideas, and that they are clauses being joined into one sentence.
Answer:Abstinence. ...
Reducing infant mortality so that parents do not need to have many children to ensure at least some survive to adulthood.
Abortion.
Changing status of women causing departure from traditional sexual division of labour.
Sterilization.
Hope these are some ideas that will help you... Stay safe and have a great Thanksgiving!!! :D