CTRL + Click for selecting multiple values

Hi! I am creating an eLearning lesson where the user is required to press and hold the CTRL key and then click values in a list with their mouse. So far, I haven't found a way to require that they both press CTRL and click. I can use the CTRL key as a shortcut instead of the click, but it doesn't require that they do both. Is there anything that I can do to simulate this process properly?

Thank you!

TLV