Hi Bianca,
The answer to this depends on whether or not you're using one of our templates. Adding a drag and drop shouldn't be too difficult, but making it work with the rest of the template (increment correct count if correct, increment incorrect count if incorrect) will take an extra step. Here's a video that shows you how to set this up. Basically you'll use a "click" step as a starting point, add in your drag item and dropzone, get the drag-and-drop functionality set up, and then when they drop it correctly or incorrectly, copy over the responses from the template.
http://share.smartbuilder.com/public/support/dnd-software-simulation.mp4Hope that helps!