多项选择题
A.-（BOOL）writeToFile：atomicallyB.-（NSString *）descriptionWithLocaleC.-（NSArray *）objectsForKeys：notFoundMarkerD.-（id）objectForKeyedSubscript
A.NSThreadB.NSOperationC.CoreDataD.GCD
A.select from table filmB.select *from table filmC.select from filmD.select *from film