1.Mom was preparing supper. Dad arrived home (when)

-> Mom was preparing supper when dad arrived home
2.The children had gone to bed. Doug and Susan planned the family vacation(after)

-> After the children had gone to bed,Doug and Susan planned the family vacation
3.Mark was home in the morning. In the afternoon, he went to the gym (but)

-> Mark was home in the morning, but in  the afternoon, he went to the gym 
4. We were talking a DVD. The lights went out (when)

->

We were talking a DVD when the lights went out 

5. We were talking a test. The fire alarm rang (while)

-> While we were talking a test ,the fire alarm rang
6. The teacher walked into the classroom. She handed out the assignments (as soon as)

-> As soon as the teacher walked into the classroom,she handed out the assignments