单项选择题

A. CREATE UNIQUE INDEX xtab1 ON tab1 (c1) include (c2)
B. CREATE UNIQUE INDEX xtab1 ON tab1 (c1);  CREATE INDEX xtab2 ON tab1 (c3) INCLUDE (c2) 
C. CREATE UNIQUE INDEX xtab1 ON tab1 (c2, c1)
D. CREATE UNIQUE INDEX xtab1 ON tab1 (c2) INCLUDE (c1)