MULTIPLE CHOICES IN SELECT BOXES: You can choose multiple choices within the select box by holding down the Control (Ctrl) Key when clicking on the EACH selection (Note: if you fail to hold down the Control Key after the first choice, your other selections will be de-selected!) You can also de-select a single choice by holding down the Control Key when you click on it.
Alternatively or adjunctively, you can select a string of consecutive choices by clicking the first choice, and then hold down the Shift Key when you click the last choice in the string. Usage of both techniques can be combined to select strings, de-select individual choices within the string, or select individual choices outside of the string.