grammatical number - "Attached {is/are} X, Y and Z." If X, Y and Z are all singular, is it correct to use "is" here?

Which is correct?

1. Attached are our compensation plan, an independent contract agreement, and a W9.




2. Attached is our compensation plan, an independent contract agreement, and a W9.

I thought because each of the items segregated by the comma was singular it should be "is".