Trying to understand conditional field logic

If I have a drop-down field that includes a list like:

• Big Green One
• Small Green One
• Big Red One
• Small Red One
• Big Green Two
• Small Green Two
• Big Red Two
• Small Red Two

And I want another field to show if the user selection is any of the Big items, can I just make one condition for when the field contains “big”–or do I have to make 4 conditions, one for each specific option?