Checkboxes changed to radio buttons.
It would be more helpful for the multiple choice questions that only want one answer to be set to radio buttons. Currently, they are checkboxes.
The way that the multiple answers part is done now is frustrating and teaches test-taking skills more than language; Only about one time in 10 are there multiple correct answers which trains you to click submit as soon as you find one right answer, and then that one time in 10 that there is more than one right answer, the rug is yanked out from under you. In these situations it is far more likely that a second right answer was ignored altogether than that the learner read the answer and decided it was wrong, so this isn't really teaching language skills so much as playing a mean trick on users of the site...