Which of the following is an example of a paired design?

A. A teacher taught one class a lesson using technology and another class without technology. Their scores on a quiz were then compared.

B. A teacher taught a lesson using technology and then compared the class scores on a quiz to the national average score.

C. A teacher teaches a lesson using technology and then gives her students a pair of quizzes and compares these results to those from her class the previous year.

D. Pairs of students were matched by similar IQs. One of the pair was taught a lesson using technology and one without technology. Their scores on a quiz were then compared.