Adding Layers to Words in a Body of Text

I would cover the sentence with a box filled with color. When clicked, it would turn to Visited state, which would contain the additional information. When the learner is finished, they click and it turns to Hidden state.

Construction details:

1. Start with the shape, fill it with highlight color, and set the transparency property to the value that looks best to you. 

2. Edit the states of the shape, copy the Normal state and call it Visited. Visited state has its own built-in trigger to change to the Visited state when clicked, so you don't need to worry about.

3. Close states editing, then build the additional information text box as you want. I envision an "X" (or something similar) on the text box for the learner to indicate they are ready to advance. Create the "X" either as part of the textbox or as a separate object. You have more ease and flexibility in positioning it if it is a separate object. Attach two triggers to the "X". The first is "Change state of [shape1] to Hidden (you don't have to create this state, it's built-in) when user clicks [shape]", and the second is "Jump to [slide name] when user clicks [shape] if the state of [shape1] is Hidden AND state of [shape2] is Hidden, and state of [shape3] is Hidden"

4. Select the textbox and "X" and copy them.

5. Edit the states of the shape (again). Select the Visited shape, and paste the box and "X" . Position them where you want them in relation to the color.