Find output

What will be the output of the following statements?
DECLARE @iRet INT
SELECT @iRet = ISNULL(@iRet,'1') + MyValue
FROM (SELECT '1' MyValue UNION SELECT '1' UNION SELECT '2') t1
SELECT @iRet

A. An error will be generated
B. '112'
C. 4
D. '1112'

Answer:[C]
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