Dropdown fields offer several options for the student to choose, and he will have the select the correct one.
Once a Dropdown field has been added, its options screen will appear. We will have to input the different options from which the student will have to choose, and which one is the correct option. We can also change the font size and color of that field, as well as its transparency if we want to see the background through the field.
For each Selector field we can add as many options as we want, but only one of them can be marked as the correct answer. By clicking on the + button we will add more options to the dropdown. We can also add new options with the keyboard, by pressing Ctrl+Intro (or ⌘+Intro in Mac).
Once all the options are added we will be able to see the field in the editor, which will show the correct answer.
Here you can see a video showing how a student will see the Dropdown field: