enum {
NSJSONReadingMutableContainers = (1UL << 0),
NSJSONReadingMutableLeaves = (1UL << 1),
NSJSONReadingAllowFragments = (1UL << 2)
};typedef NSUInteger NSJSONReadingOptions;
數組中含以上三種參數，
第一種：
NSJSONReadingMutableContainers
Specifies
that arrays and dictionaries are created as mutable objects.
是說被創建的數組或者字典應該是可變的
第二種：
NSJSONReadingMutableLeaves
Specifies that leaf strings in the JSON object graph are created as instances of NSMutableString.
是說JSON對象中的被創建的字符串是NSMutableString類型的
第三種：
NSJSONReadingAllowFragments
Specifies that the parser should allow top-level objects that are not an instance of NSArray or NSDictionary.
這一句是說解析出的頂層對象可以允許不是NSArray或NSDictionary類型的