Which of the Following Is the Best Example of a Cross-Sectional

Which of the following is the best example of a cross-sectional research study?

A) Each year the five-year-olds of Ontario are given number and letter proficiency exams before they begin kindergarten.
B) Dr. Sanchez assessed the eye-hand coordination of the second, fourth, and sixth graders of Maple Leaf Elementary School in December 2001, 2003, 2005, and 2007.
C) A number of graduate students studied the playground interactions of two classes of fourth graders by secretly videotaping the playground activities from the third-floor window of an adjacent building.
D) Dr. Huang assessed the eye-hand coordination of the second, fourth, and sixth graders of Maple Leaf Elementary School in September 2001.