human
Solve the following python programming problem given the following code:
@ classmethod 
def _handle_incoming_event(cls, active_realtime_layer, event_type, * args) : 
    exp_id = args [0] 
    def _increment_visit_counter() : 
        realtime_class = cls._get_realtime_datastore_class () 
        realtime_model_id = realtime_class.get_realtime_id (active_realtime_layer, exp_id) 
        model = realtime_class.get (realtime_model_id, strict = False) 
        if (model is None) : 
            realtime_class (id = realtime_model_id, num_starts = 1, realtime_layer = active_realtime_layer).put () 
else : 
            model.num_starts += 1 
            model.put () 
def _increment_completion_counter() : 
        realtime_class = cls._get_realtime_datastore_class () 
        realtime_model_id = realtime_class.get_realtime_id (active_realtime_layer, exp_id) 
        model = realtime_class.get (realtime_model_id, strict = False) 
        if (model is None) : 
            realtime_class (id = realtime_model_id, num_completions = 1, realtime_layer = active_realtime_layer).put () 
else : 
            model.num_completions += 1 
            model.put () 
if (event_type == feconf.EVENT_TYPE_START_EXPLORATION) : 
        transaction_services.run_in_transaction (_increment_visit_counter) 
else : 
        transaction_services.run_in_transaction (<MASK>) 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: active_realtime_layer, exp_id, args, _increment_visit_counter, cls, event_type
assistant
#Here is a proper replacement for <MASK>.
def _increment_completion_counter(