Select multiple items in a cell from a list

Hi,

I am new to MS Excel and need to be able to select multiple items in a cell from a list. I tried to use data validation but it allows me to choose only a single item from a list. Could you suggest an easy step-by-step way to select from a list multiple items in a cell?

If there’s no easy way to do so (my computer skills are quite limited), could you please help with the attached excel sheet? I’d like to have a drop-down menu on column C that will enable me to choose multiple items in each cell of that column among the set of items that are in column B. Likewise (although less important), I’d like I’d like to have a drop-down menu on column E that will enable me to choose multiple items in each cell of that column among the set of items that are in column D.

Thank you very much,

Hopper8