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A ___ Key in Table 1 that refers to the Primary Key in Table 2 must either have null values or be available in Table 2. This is what Referential Integrity constraints require

18. A ___ Key in Table 1 that refers to the Primary Key in Table 2 must either have null values or be available in Table 2. This is what Referential Integrity constraints require.

1. Primary
2. Alternate
3. Foreign
4. Composite

Answer: C) Foreign

Explanation:

A Foreign Key in Table 1 that refers to the Primary Key in Table 2 must either have zero values or be available in Table 2. This is what Referential Integrity constraints require.