Select the correct passive form of the given sentence.
A twenty-year-old boy was taking science classes for children.
1
Science classes for children were being taken by a twenty-year-old boy.
2
Children for science classes were being taken by a twenty-year-old boy.
3
Science classes for children were taken by a twenty-year-old boy.
4
Science classes for children had been taken by a twenty-year-old boy.