Comprehensive and Detailed Explanation From Exact Extract:

This is a classic application of theDecision Table Testingtechnique.

We are combining two conditions:

Purchase Volume, which has3 equivalence classes:

1 to 100 units → 0%

101 to 1000 units → 5%

More than 1000 units → 10%

Customer Type, which has2 categories:

Frequent Customer = YES → 5% extra

Frequent Customer = NO → 0%

This gives:

3 (bulk discount levels) × 2 (frequent customer options) = 6 unique decision rules

Each combination of these input conditions defines a separate test scenario with its own outcome.

“Decision table testing is used to identify the different combinations of inputs and their associated outputs. Each unique combination of input values defines a rule.”

(ISTQB CTFL Syllabus v4.0, Section 4.2.3 – Decision Table Testing, Page 40)

Thus,Option D (6 decision rules)is the correct answer.