Answer:
c. matched pairs design.
Explanation:
For an experimental design to be classified as matched pairs, it must have two treatment options and the grouping of participants with common demographics. The participants can be either grouped in pairs or within ranges. Grouping participants within ranges makes the assignment to groups less tedious compared to when they are in pairs. The test above employs this design because,
1. It tests the effectiveness of two new treatments for stomach ulcers
2. The subjects are grouped within ranges based on the age demographic factor.