As shown in the figure, the shape of a test field is a triangle (let it be △ ABC). The administrator starts from a point D on the side of BC, walks a circle in the direction of DC ﹥ Ca ﹥ ab ﹥ BD, and comes back to D. then the administrator starts from the starting point to the original place and returns to the original place on the way () A. Turn 90 ° B. turn 180 ° C. turn 270 ° D. turn 360 ° C

As shown in the figure, the shape of a test field is a triangle (let it be △ ABC). The administrator starts from a point D on the side of BC, walks a circle in the direction of DC ﹥ Ca ﹥ ab ﹥ BD, and comes back to D. then the administrator starts from the starting point to the original place and returns to the original place on the way () A. Turn 90 ° B. turn 180 ° C. turn 270 ° D. turn 360 ° C

The administrator walks forward, and the sum of the turning angles is exactly the outer angle and 360 degree of the triangle