Passing Multiple Values or a Range to a Crystal Report

I'm usinf VB.Net 2010 (pro), the report was created with CR XI and the CrystalDecisions version is 13.x

I'm creating a report "broadcaster" application.  Basically the app will take in a list of reports, the email addresses of those who are subscribed, values for parameters and days/times of sending.

Everything is fine except the parameters.  A couple of the reports have, potentially, a list of values (like department names).  In the report itself, this is a listbox showing all possibilities, and another listbox that allows you to add one or more items from the first listbox.  Hopefully you know what I'm talking about.

How do I do this in code, though?

For example, if I want to show records for department ABC, I know I can do this:

myReportDocument.SetParameterValue("DeptName", "ABC")

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But what happens if I want to show records for department ABC, DEF and GHI?

Would I do this:

myReportDocument.SetParameterValue("DeptName", "ABC")
myReportDocument.SetParameterValue("DeptName", "DEF")
myReportDocument.SetParameterValue("DeptName", "GHI")

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Or this:

myReportDocument.SetParameterValue("DeptName", "ABC,DEF,GHI")

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Or something completely different?

TIA