Identify the type of sampling used (random, systematic, convenience, stratified, or cluster sampling) in the situation described below.

A woman experienced a tax credit. The tax department claimed that the woman was audited because everyone in four randomly selected districts was being audited.

Which type of sampling did the tax department use?
A. Cluster sampling
B. Systematic Sampling
C. Convenience Sampling
D. Random Sampling
E. Stratified Sampling