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若U={1,2,3,4}, M={1,2},N={2,3}, 则
(A) {1,2,3} (B) {4} (C) {1,3,4} (D) {2}
A.{1,2,3}
B.{2}
C.{1,3,4}
D.{4}
若U={1,2,3,4}, M={1,2},N={2,3}, 则 ( )
(A) {1,2,3} (B) {2} (C) {1,3,4} (D) {4}