✔ 最佳答案
When you paste the new slides into the existing presentation, look at the end or bottom of what you pasted (depending if you pasted into slide sorter or the left-side preview in the work view). You should see a little clipboard type icon, go to its pulldown menu and select Keep Source Formatting. Not only will it hold the original format and background, but it will bring the Master with it so you can apply it to any new slides if you want.