Which of the Following Describes a Sequential Design

Which of the following describes a sequential design?

A) Studying a group of 5 year olds over a 10 year period
B) Comparing reasoning abilities of 5, 8, and 10 year-olds
C) Measuring motor abilities of a child when she is 2 years old and then measuring her abilities again when she is 5 years old
D) Studying groups of 10- and 15-year-olds, and then studying these individuals 2, 4, and 6 years later