The type of research design which compares various participants at several points in time (no longer than 6 years apart) to examine age-related differences and changes is called a .

cross-sequential design

Explanation:

Cross-sequential design -

This method of study uses both the cross-sectional design as well as the longitudinal design .

It refers to the type of study where comparison is done between two or more than two groups over a particular period of time , is referred to as cross - sequential design .

The method is beneficial to detect or analyse any error in the either of the design individually .

Hence , from the given information of the question ,

The correct answer is cross - sequential design .

pretty sure a is right