human
Solve the following python programming problem given the following code:
def __call__(self, environ, start_response) : 
    script_name = environ.get ('SCRIPT_NAME', '') 
    path_info = environ.get ('PATH_INFO', '') 
    sent = [] 
    written_response = StringIO.StringIO () 
    def replacement_start_response(status, headers, exc_info = None) : 
        if (not self.should_filter (status, headers)) : 
            return start_response (status, headers, exc_info) 
else : 
            sent [:] = [status, headers, exc_info] 
            return written_response.write 
app_iter = self.app (environ, <MASK>) 
    if (not sent) : 
        return app_iter 
(status, headers, exc_info) = sent 
    try : 
        for chunk in app_iter : 
            written_response.write (chunk) 
finally : 
        if hasattr (app_iter, 'close') : 
            app_iter.close () 
body = written_response.getvalue () 
    (status, headers, body) = self.filter (script_name, path_info, environ, status, headers, body) 
    start_response (status, headers, exc_info) 
    return [body] 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: path_info, environ, sent, headers, self, chunk, app_iter, exc_info, status, start_response, script_name, body, written_response
assistant
#Here is a proper replacement for <MASK>.
def replacement_start_response(