Let $R (a, b, c)$ and $S(d, e, f)$ be two relations in which $d$ is the foreign key of $S$ that refers to the primary key of $R$. Consider the following four operations $R$ and $S$
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Insert into $R$
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Insert into $S$
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Delete from $R$
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Delete from $S$
Which of the following can cause violation of the referential integrity constraint above?
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Both I and IV
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Both II and III
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All of these
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None of these