Among the restaurants being inspected in 2016, how many of them are in San Francisco?
inspected in 2016 refers to YEAR(date) = 2016; San Francisco refers to city in ('San Francisco', 'SF' ,'S.F.', 'SAN FRANCISCO');
SELECT COUNT(DISTINCT T2.business_id) FROM inspections AS T1 INNER JOIN businesses AS T2 ON T1.business_id = T2.business_id WHERE STRFTIME('%Y', T1.`date`) = '2016' AND T2.city IN ('San Francisco', 'SAN FRANCISCO', 'SF', 'S.F.')