Consider the Following to Answer the Question(s) Below

Consider the following to answer the question(s) below.
ASW, a regional shoe chain, has recently launched an online store. Sales via the Internet have been sluggish compared to their brick and mortar stores, and management suspects that its regular customers have concerns regarding the security of online transactions. To determine if this is the case, they plan to survey a sample of their regular customers.
-Suppose that ASW has an alphabetized list of regular customers who belong to their rewards program. After randomly selecting a customer on the list, every 25th customer from that point on is chosen to be in the sample. This sampling plan is called

A) Simple Random Sampling
B) Stratified Sampling
C) Cluster Sampling
D) Systematic Sampling
E) Convenience Sampling