Hi Grazzers,
Its very good morning for me, I tried 2 days for your solution at last today I got the solution.
Do like this, take an extra field and put a rule on the Activity drop down that if the Activity drop down is not blank then set the fields value as extra field = Activity drop down value.
Now filter the second drop down Analysis value by comparing as Activity field value in the xml is equal to extra field value.
You will get the solution, still have doubt please let me know.
Have a nice day.