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What is the result of the following batch?

DECLARE @Test TABLE(a INT IDENTITY, b VARCHAR(5))
DECLARE @sRet VARCHAR(255)
SET @sRet = 'Happy'
SELECT @sRet = ISNULL(b, '!') FROM @Test ORDER BY a
INSERT @Test VALUES('Happy')
INSERT @Test VALUES('Lunar')
INSERT @Test VALUES('New')
INSERT @Test VALUES('Year')
SELECT @sRet = @sRet + ' ' + b FROM @Test ORDER BY a
SELECT @sRet

A. NULL
B. ! Happy Lunar New Year
C. An error will be generated
D. Happy Happy Lunar New Year
E. Happy Lunar New Year

Answer:[D]
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