If Some Natural Relationship Exists Between Each Pair of Observations

If some natural relationship exists between each pair of observations that provides a logical reason to compare the first observation of sample 1 with the first observation of sample 2, the second observation of sample 1 with the second observation of sample 2, and so on, the samples are referred to as:

A) matched samples.
B) independent samples.
C) weighted samples.
D) random samples.