ITMC 2018 Grade 10 National Preliminary set01 Question 1

Question 1

Printed positive marks are preserved per question. The source uses different blank-answer and incorrect-answer rules by section, including an optional bonus penalty; the import does not reproduce that complete official scoring scheme.

Let $A,B$ be sets. Which set expression is different from the others? A prime denotes complement.

$(A-B)^{\prime}$
$A^{\prime}\cup B$
$(B^{\prime}-A^{\prime})^{\prime}$
$B-A$
$(B^{\prime}\cap A)^{\prime}$