A.2 B.0.2 C.±2 D.-0.2
A.30cm B.20cm C.10cm D.5cm
A.1/K=(D返-D往/D) B.(1/│K│)=(D返-D往/D) C.1/K=(│D往-D返│/D) D.-1/K=(D往-D返/D)