human
Solve the following python programming problem given the following code:
@ classmethod 
def QueryActivities(cls, client, viewpoint_id, callback, excl_start_key = None, limit = None) : 
    "Queries activities belonging to the viewpoint (up to 'limit' total) for
    the specified 'viewpoint_id'. Starts with activities having a key greater
    than 'excl_start_key'. Returns a tuple with the array of activities and
    the last queried key.
    " 
    def _OnQueryActivities(activities) : 
        callback ((activities, (activities [(- 1)].activity_id if (len (activities) > 0) else None))) 
Activity.RangeQuery (client, viewpoint_id, range_desc = None, limit = limit, col_names = None, callback = <MASK>, excl_start_key = excl_start_key) 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def _OnQueryActivities(