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A为ADS中的普通表，a为A的分区列，类型为bigint，b为A中的普通列，类型为bigint，请判断以下相关SQL中()语法是错误的。

（A）SELECT a FROM A ORDER BY a LIMIT 100

（B）SELECT a+b, count(a) FROM A group by a+b ORDER BY a

（C）SELECT a,b FROM A ORDER BY a+b LIMIT 100

（D）SELECT a, count(a) FROM A group by a ORDER BY a