Unobtrusive measures: a. A process in which numbers are assigned according to rules of correspondence between definitions and observations. b. The study of physical traces, archives, and observation without participation. c. The process of figuring out how to measure concepts using empirical evidence. d. The challenge of collecting data without it being affected by certain external obstructions.

Which statement explains how you could use coordinate geometry to prove the opposite sides of a quadrilateral are congruent? a. use the slope formula to prove the slopes of the opposite sides are the same. b. use the slope formula to prove the slopes of the opposite sides are opposite reciprocals. c. use the distance formula to prove the lengths of the opposite sides are the same. d. use the distance formula to prove the midpoints of the opposite sides are the same.