activity diagram - how to show multiple objects passed between two actions?

Question

Background

I have one action (action_a) that calls an operation(operation_x) on another action (action_b).

The parameters to operation_x are as follows:

action_b.operation_x( param_1, param_2 )

I'm trying to work out how to document the parameters being passed in UML activity diagrams.

Option 1

One option may be to use a comment?

Option 2

Another option may be to use activity parameters, but it doesn't seem right to show two flows from action_a for one operation call?

Question

How can I show multiple objects being passed?

Answer 1

Option 2 is close, but the edges coming out of action_a are not right, and I don't think it's legal to show the call and the details on the same diagram. Please see my other answer.