Crystal Reports Multiple Maximum fields for groups

Message

     I have a sub-report where I am grouping by an ID field (Opportunity.ID). The primary reason for this is that I want to display the last activity associated with that opportunity. So in the Group Selection formula, I have:

{HISTORY.COMPLETEDDATE} = Maximum({HISTORY.COMPLETEDDATE}, {OPPORTUNITY.ID})

This works like a charm.

The problem now is that I also need to show the next activity related to this opportunity - so the Maximum(ACTIVITY.STARTDATE).

Is it possible to select more than one maximum field, and if so, what would the syntax look like? 

Thanks