Louis:
I have added the ability to uncheck the radio buttons, either by clicking them a second time, or shift-clicking them (the problem author specifies which). You need to set an additional option for the RadioButtons() function: either uncheckable=>1 or uncheckable=>"shift".
Note that this requires the user to have JavaScript active. It is possible for students to have JavaScript turned off, and so unchecking would not be possible in that case. Currently no message is issued, but it would be possible to have a message added to the problem to warn the user that they would be able to uncheck the buttons if they turned on JavaScript.
Davide
WeBWorK Problems
Scoring a Multiple Choice Problem
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