How do I disable a dropdown list in a Side-by-Side question?

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I have the above side-by-side question and i would like to disable users to make changes to column.
Tried several jQuery but to no avail.

var qid = this.questionId;
$('QR~'+qid+'#2~1~1').up('td').childElements().attr('disabled','disabled');
$('QR~'+qid+'#2~1~1').up('td').childElements().prop('disabled','disabled');

Need advice, please! thank you in advance.