How to get user to select all correct choices before continuing.

This post has info and a demo file that explains/shows how to track answers so you can customize feedback and/or branching: https://community.articulate.com/discussions/articulate-storyline/tip-track-responses-to-custom-questions-or-surveys 

Update. Solved my issue. Created a Selected/Normal toggle feature and coded the submit button to check for Selected/Normal states on each answer before sending the learner to the correct or incorrect landing slide.

FYI: Built-in states come with built-in functionality.

Any object with a Normal state and a Selected state will automatically toggle between those two states when clicked—without any triggers.

• Thus, you don't need those triggers that toggle between the states.

The exception: If you put multiple objects with Normal and Selected states into a Button Set, selecting one will automatically deselect the others. In other words, you can only select one at a time (as in a Multiple Choice question).

• There's no way to deselect all of them after the first one has been clicked, unless that's done with a trigger. But since this is how a button set should work, I'd say there's no need for such a trigger.
• Here's the User Guide info on Button Sets: https://community.articulate.com/series/articulate-storyline-360/articles/articulate-storyline-360-user-guide-how-to-work-with-button-sets  

In my experience, as well as based on what I've seen in the Forum, it's best to let the built-in functions work on their own. In other words, don't add triggers that duplicate what will already happen. That might cause problems.

Also, it's more stable to use "≠ Selected" ("is not Selected") as a condition, instead of "=Normal" ("is Normal"). As Hero Walt Hamilton once put it: like us, every state thinks it's Normal. In other words, Normal underlies every state, so an "=Normal" condition doesn't always work as expected.