The question is about selecting the correct test values for x based on equivalence partitioning. Equivalence partitioning is a software test design technique that divides the input data of a software unit into partitions of equivalent data from which test cases can be derived. In this case, the given equivalence classes are:

(x \leq -100)

(-100 < x < 100)

(100 \leq x < 1000)

(x \geq 1000)

Option D provides a value from each of these partitions:

For (x \leq -100), it gives -1000.

For (-100 < x < 100), it gives -100 and 100.

For (100 \leq x < 1000), it gives 500.

For (x \geq 1000), it gives 1500.

So, option D covers all four given equivalence classes with appropriate values.

References: ISTQB Certified Tester Foundation Level (CTFL) v4.0 documents available at ISTQB and ASTQB.

1: ISTQB Foundation Level Syllabus 2018, Version 4.0, p. 38

2: ISTQB Foundation Level Syllabus 2018, Version 4.0, p. 39

: ISTQB Foundation Level Syllabus 2018, Version 4.0, p. 40