What is a primary source? A. A textbook that explains a wide range of science topics
B. A technical article written by an experimenter
C. A newspaper article about a recent discovery
D. A summary of research written for an average reader

Arunner is training for an upcoming marathon by running around a 100-m-diameter circular track at constant speed. let a coordinate system have its origin at the center of the circle with the x-axis pointing east and the y-axis north. the runner starts at (x, y) = (50 m, 0 m) and runs 2.5 times around the track in a clockwise direction.