One method to check a laser for level begins by choosing two surfaces approximately 15' apart to use as targets. Then, with the instrument 6" away from target 1, mark the center of the line (A1). Swivel the laser __________, and mark the center of the line on target 2 (B1). Repeat the process by moving the laser the same distance from target 2 and marking the center of the line (B2), then swivel the laser 180, and mark the center of the line on target 1 (A2). a. 90 b. 180 c. 270 d. 360