You can do an "Invisible Continue"
- Make a Topic and Response (as normal)
- Make a second but leave the Topic blank, just fill in your NPC's Response
Back in Dialogue View, join the two Topic Blocks as normal
Then right click on the join line and select "Invisible Continue" - The NPC will say the second line as soon as it has finished the first
You can chain together as many as you want in that way