在Oracle中，下列哪些条件分支语句是正确的？ A select CASE Ssex WHEN '男' THEN '帅哥' WHEN '女' THEN '美女' ELSE 'unknown' END des from Student; B select CASE Ssex WHEN '男' THEN '帅哥' WHEN '女' THEN '美女' ELSE 'unknown' from Student; C select CASE WHEN Ssex='男' THEN '帅哥' WHEN Ssex='女' THEN '美女' ELSE 'unknown' END des from Student; D select CASE Ssex WHEN '男' THEN '帅哥' WHEN '女' THEN '美女' END des from Student;