Need Help-Struggling to create this activity in storyline. Any ideas would be appreciated

I think this would be easier to do with a set of radio buttons for each "blank." To prevent the screen from being too cluttered, have each set be presented separately.

For example, you could take the user through layers. On the first layer, they'd select the button for Type of Activity, and the next layer would have the Audience buttons, etc. (Or those selections could be done on separate slides.) 

In either case, clicking a given button could adjust the value of an associated variable. So you could also show how their choices build into the completed sentence by displaying the variable references.