Drop Down Values

[kgcognos]

I have a year parameter. I only want the (current year and previous year) OR (current year and next year) depending on the current month to show on the drop down.
Please help on how I can accomplish this. What prompt property setting should I change?

Also, I'm trying to get the current year. I'm using cast(extract(year,current_timestamp),varchar(4)) in the report expression but the validation keeps on failing. How do I extract a year in Report Expression when defining a variable? 
Thank you in advance.