The 'select box' answer type for multiple choice questions seems to default to a size of 10. If you only have a few responses to choose from it might not make sense to keep the size=10 (number of rows shown). Below is a example with the size property set at 3.

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To set the size property for the select box, simply add the following code to your 'addOnReady' function in the javascript editor of your select box question:

var qid = this.questionId;
jQuery( "select[name='QR\\~"+qid+"']" ).prop("size",3); // using 'qid' so you can simply copy and paste this code into other similar questions without needing to hard-code the question ID; setting the size=3

Note: The select box is useful if you wish to use 'in-page' display logic using the responses from this question type (answer choices such as dropdown do not seem to allow for in-page display logic) and where the tab key is mainly used to move through the survey and keyboard keys such as numbers are used to select the response options (where something such as a radio button group would require tabbing through each response option which can be inefficient).